Why do I get 800A01CA errors?

Microsoft VBScript Runtime error '800a01ca'  Variable uses an Automation type not supported in VBScript

 
If you are returning a numeric value from a database, make sure you convert it to a long or double before attempting to use it for calculations (see KB #195180). 
 
If you have a custom COM object, make sure you are passing valid OLE automation datatypes back and forth (e.g. those that can be supported as VARIANTs under VBScript). If you are using a BSTR as an [out] parameter, for example, you might come across this error. One workaround would be to use an [out,retval] parameter instead. 
 
You might have a simple typo, e.g. the following code would produce this error: 
 

<%      response.write "foo = " &       rs("foo")  %>

 
Obviously, it seems like you are trying to call a method rs("foo") when it is in fact returning a string. Of course, those two strings should either be on the same line, or concatenated by a proper line delimiter, e.g.: 
 

<%      response.write "foo = " & rs("foo")        ' or        response.write "foo = " & _          rs("foo")  %>