APP-FND-01926: The custom event WHEN-LOGON-CHANGED raised unhandled exception: ORA-06508: PL/SQL: could not find program unit being called

This issue has been observed under the following circumstances:

CUSTOM.plx file are of different date than the conversion date (last compilation date), the likeky reason for this is that CUSTOM.pll has not been properly compiled.
For example:
-rwxr-xr-x    1 oradev   dba           24576 Aug 24 2009  CUSTOM.pll
-rwxr-xr-x    1 oradev   dba           20480 Mar 31 12:36 CUSTOM.plx



To implement the solution, please do the following:
1. Take a backup of both files CUSTOM.PLL and CUSTOM.PLX
2. Get a working copy of the custom.pll file.
3. Compile the custom.pll using f60gen under the environment which creates the file custom.plx, where the last access date shows the current date.

f60gen \
module=$AU_TOP/resource/CUSTOM.pll \
userid=APPS/xxx \
output_file=$AU_TOP/resource/CUSTOM.plx \
module_type=library batch=yes compile_all=special

4. The $FORMS60_PATH needs to be in sync with the value set for the s_f60path variable in the Context.xml file.
i.e  >/oracle/apps/test10appl/au/11.5.0/resource:/oracle/apps/test10appl/au/11.5.0/resource/stub</FORMS60_PATH>

5. Run Autoconfig to instantiate the changes.

Ref:11i: "APP-FND-01926: The custom event WHEN-LOGON-CHANGED raised unhandled exception" Error When Attempting to Launch Forms (Doc ID 1080160.1)