fetch serialized object failed

Working in Sales Order Entry - Sales Order Detail Revisions, we get the following error message:
COULD NOT LOAD FORM: P3210_W3210B_AM010019
JAS_MSG431 : Fetch serialized object failed. Please contact your system administrator.
This is in JPY812, toolset 8.96C. It works in JDV812. I treid to build a package with P3120 in it for PY, but it didn't fix the problem.

And you java genned it to JPY812 too right? Did you then clear the cache on the JAS server?