It sounds very much like the OQA code has been modified or custumized and the customizations are expecting a different type of value– or are expecting a value and getting a NULL.
This sounds like a problem deep inside your installation of OWA. I’ve seen similar situations where OQA was customized to support more than one (the default) contact form and a servcie pack broke the customizations.
In asp/ASp.NET/VBSCRIPt a type mismatch is an error where a variable is passed to a function or subroutine that was expecting a different type of value. For example, passing a string (“mystring”) when a number is expected (1002) by the function.