Hi. Im having the same issue.
I used latest SA2 before I had purchased and installed CSS Form Builder 2. SA 2 was using Validation Toolkit for Spry code on form fields and it worked without a problem. Then I installed CSS Form Builder 2, now SA is using form builders Spry code on form fields and Im getting the errors in IE, but all other browsers work with a problem.
I compared the code between files generated without CSS form Builder installed and with CSS Form Builder installed.
The old files in the head section of the files refer to ValidationToolkit/..php files
But with CSS Form Builder refer to webassist/forms/..php
I changed my files to refer to ValidationToolkit and it seems to work.
It may help, but not entirely sure what could be the cause.