Why do I get errors in the 800A03F1 -> 800A03FF range?

Most of these errors can be caught rather easily by either inspecting the line indicated, or poring over the script looking for invalid nesting or missed couplings. It may take some work, depending on the length and complexity of the code. This is one of the reasons I am a huge proponent for nicely indented code. Anything inside a loop, or an if, or select case, or do while, etc. should be indented to make the logical flow and the functional aspects of the code plainly visible — and more importantly, to make it easy to spot the beginning and end of each construct. There is no excuse for the following (and yes, I've seen code almost exactly like this, though much longer): 
 

<%  if not rs.eof then  do while not rs.eof  if rs(0) = "foo" then  response.write "bar"  for i = 0 to rs(1)  response.write i & ","  next  end if  rs.movenext  loop  else  response.write "no records"  end if  %>

 
So, now that you're going to go back and indent your code nicely, you can quickly find the solution to the errors in this range... 
 
 

Microsoft JScript compilation error '800a03f1'   Expected '}'

 
This error is pretty straightforward; you have an opening curly brace({) without a matching end curly brace (}). Here is some trivial code to reproduce: 
 

<script language=jscript runat=server>  function foo()  {  </script>

 
 

Microsoft VBScript compilation error '800a03f2'   Expected identifier    or    Microsoft JScript compilation error '800a03f2'   Expected identifier

 
This usually means you tried to create a variable using a reserved word. 
 

<%      dim class  %>

 
or 
 

<script language=jscript runat=server>  var throw;  </script>

 
You'll need to avoid reserved words for naming variables. See the following Knowledge Base article for a complete list of current reserved words in VBScript and JScript: 
 
    KB #216528  INFO: Reserved Words in VBScript 5.5 and JScript 5.5 
 
Another scenario is that you tried to use the OPTIONAL keyword in a function or sub, e.g.: 
 

<%      function foo(optional bar)          ' do something      end function  %>

 
See Article #2349 for some viable workarounds. 
 
And finally, you might have a long DIM statement with a syntax error, e.g.: 
 

dim var1, var2, , var3, var4

 
 

Microsoft VBScript compilation error '800a03f3'   Expected '='

 
This is another fairly straightforward error message. Look at the line implicated, and it probably has something like this (a missing assignment operator, or forgetting to put underbars in a constant name): 
 

<%      set rs conn.execute(sql)      const ADS GROUP TYPE UNIVERSAL GROUP = &h00000008  %>

 
Should be: 
 

<%      set rs = conn.execute(sql)      const ADS_GROUP_TYPE_UNIVERSAL_GROUP = &h00000008  %>

 
 

Microsoft VBScript compilation error '800a03f4'  Expected 'If'

 
This error is probably indicating that you have used an END statement without the associated IF, or have improperly nested things. Here are a few repros: 
 

<%      if a = 1 then          response.write "blat"      end    ' or        sub foo          if a = 1 then              b = 1      end sub    ' or        sub foo          if a = 1 then              end sub      end if  %>

 
 

Microsoft VBScript compilation error '800a03f5'   Expected 'To'

 
The line number should point you straight to this one. Look for something like this: 
 

<%      for i = 1  %>

 
You need to tell the loop construct when to end, e.g. 
 

<%      for i = 1 to 10  %>

 
 

Microsoft VBScript compilation error '800a03f6'   Expected 'End'

 
Very similar to above, this should be easy to spot, provided that you have nicely indented code. Here are some snippets that reproduce the problem: 
 

<%      if a = 1 then          response.write "blat"    ' or        sub blat          ' do something    ' or        select case foo          case 1              ' do one thing          case 2              ' do two things  %>

 
 

Microsoft VBScript compilation error '800a03f7'  Expected 'Function'

 
You used 'end' to close a function, like the following: 
 

<%      function foo(bar)          ' do something      end  %>

 
Should be: 
 

<%      function foo(bar)          ' do something      end function  %>

 
Another variation of this error message: 
 

Microsoft JScript compilation error '800a03f7'  Unterminated string constant

 
Like the error suggests, the line indicated has a string that is incomplete, e.g.: 
 

<script language=jscript runat=server>  var foo = "bar;  </script>

 
 

Microsoft VBScript compilation error '800a03f8'  Expected 'Sub'

 
Like the previous error, you used 'end' to close a sub, such as: 
 

<%      sub foo          ' do something      end      ' should be:      ' end sub  %>

 
 

Microsoft VBScript compilation error '800a03f9'  Expected 'Then'

 
If you are used to writing in T-SQL or JScript, this one might bite you in VBScript. Your code probably looks like this: 
 

<%      if a = 1          ' do something      end if  %>

 
It should be: 
 

<%      if a = 1 then          ' do something      end if  %>

 
 

Microsoft VBScript compilation error '800a03fa'  Expected 'Wend'

 
This falls under a familiar category: you used the wrong (or no) terminator for a while loop. Here is an example: 
 

<%      while not rs.eof          ' do something          rs.movenext      loop  %>

 
Should be: 
 

<%      while not rs.eof          ' do something          rs.movenext      wend  %>

 
 

Microsoft VBScript compilation error '800a03fB'  Expected 'Loop'

 
Perhaps the inverse of the above: 
 

<%      do while not rs.eof          ' do something          rs.movenext      wend  %>

 
Should be: 
 

<%      do while not rs.eof          ' do something          rs.movenext      loop  %>

 
 

Microsoft VBScript compilation error '800a03fc'  Expected 'Next'

 
And again, you are missing a terminator for a 'for' loop. e.g.: 
 

<%      for i = 1 to 10          ' do something  %>

 
Should be: 
 

<%      for i = 1 to 10          ' do something      next  %>

 
 

Microsoft VBScript compilation error '800a03fd'   Expected 'Case'

 
This usually means one of two things. Either you have an execute without attaching it to the connection object, e.g.: 
 

<%      set conn = CreateObject("ADODB.Connection")      set rs = execute("SELECT column FROM table")  %>

 
(In this case, VBScript is trying to execute the string "SELECT column FROM table," rather than passing it along to the database to evaluate.) 
 
Should be: 
 

<%      set conn = CreateObject("ADODB.Connection")      set rs = conn.execute("SELECT column FROM table")  %>

 
Or perhaps you inadvertently threw a SQL statement into the source code (maybe during debugging): 
 

<%      SELECT column FROM table ...  %>

 
You should add a comment to the beginning of the line, or remove it altogether. 
 
 

Microsoft VBScript compilation error '800a03fe'  Expected 'Select'

 
This can happen if you have some bizarre nesting of if/end if and select structures. For example: 
 

<%      if blat = 1 then          select case something              case 1                  ' do something      end if  %>

 
Should be: 
 

<%      if blat = 1 then          select case something              case 1                  ' do something          end select      end if  %>

 
 

Microsoft JScript compilation error '800a03ff'  Expected hexadecimal digit

 
You can get this error when using FileSystemObject, and doing this: 
 

var fs = fso.OpenTextFile("c:\path\file.mdb");

 
Remember that the backslash (\) is an escape character in JScript, so you need to double these characters up, in order to escape them, so that the engine can properly evaluate the path: 
 

var fs = fso.OpenTextFile("c:\\path\\file.mdb");