Why do I get 800A003E / Input past end of file errors?

Microsoft VBScript runtime error '800a003e'  Input past end of file

 
To reproduce this error, simply create an empty (0 kb!) text file called a.txt, and place it in the same folder as the following ASP script: 
 

<%      set fso = CreateObject("Scripting.FileSystemObject")      set fs = fso.opentextfile(server.mappath("a.txt"))      f = fs.readall()      fs.close: set fs = nothing: set fso = nothing  %>

 
To fix, you can simply check the size first: 
 

<%      set fso = CreateObject("Scripting.FileSystemObject")      set fil = fso.getFile(server.mappath("a.txt"))      if fil.size > 0 then          set fs = fso.opentextfile(server.mappath("a.txt"))          f = fs.readall()          fs.close: set fs = nothing      else          f = "File was empty"      end if      set fil = nothing      set fso = nothing        response.write f  %>

 
This can also happen if you use the less efficient readline, and forget to use a while not fs.AtEndOfStream loop.