>I understand there is differences in the versions.
Yes, DisclaimIt 4.x is a completely new implementation. It doesn't contain any code from 3.x.
>Is there a workaround for this?
Not with DisclaimIt 4.x. While it would be possible to add support for messages with non-standard IPM message classes to a future version, I'm vary of going this way because you don't just know what's the content of such messages. For more information about restrictions and risks of using a global custom form, please read http://support.microsoft.com/kb/241235/en-us .
I would suggest that the company reconsiders the use of their global custom form. Do they still know why they implemented this solution many, many years ago? ;-)
-Franz