In Forms 11g and 11gR2 (especially in Windows Server 2008 R2 64-bit), there has been a case where starting a form in a Forms application using WebUtil causes the following error:
“FRM-40735: WHEN-CUSTOM-ITEM-EVENT trigger raised unhandled exception ORA-06508”

Solutions:

1. Open any affected forms in Forms Builder and re-attach webutil.pll (delete the attached library and add it again). After that, save and compile the form(s). Next, try running the application again and the problem should be resolved.

2. Remove any PLXs from the FORMS_PATH after the PLLs are compiled.

3. This error has occurred sometimes after upgrading from an older Forms 11g version to a newer one (e.g. 11.1.2.0.0 to 11.1.2.2.0). Running a recompile of your entire application has also been known to fix the problem.

NOTE: In Linux only, it has been found that for solution 2, the case is the exact opposite: PLLs should be removed and only PLXs should be removed.