from the microsoft web site:
http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q173741&
Cause
The following conditions cause the error to occur:
The elements of the submitting form are not named. For example, instead of .
The form must have a "Input" or "Select" element. In other words, the form must pass values associated with the "Input" or "Select" tags to the server.
You have code that accesses the Forms Collection from a second Active Server Pages (ASP) page. For example, the "Action" parameter of the "Form" tag points to an .asp file other than itself. And the code accesses the forms collection via 'Request.Forms("var")'. NOTE: at this time we have been unable to reproduce the error when the "Action" parameter points to itself -- the .asp file in which the form is defined.
You have code that accesses memory; as in, 'Session("variable")=value'. This condition is very touchy, sometimes just changing the name of the variable will remove the symptoms.
Resolution
Name each element--including the form itself--in the form.
-or-
Change the name of the variable, see condition 4 in the CAUSE section above.