Apex, version 3.2.1.00.10, on a 10.2.0.3-database is working fine for some time.
Then, while clicking the ‘application builder’ home-page, we got the ‘page not found’-error in the browser.
Logging of Apache shows:
mod_plsql: /pls/apex_schd/f HTTP-404 ORA-03113: end-of-file on communication channel\n
mod_plsql: Unable to reset state for mode 0: Err 3114 url=>/pls/apex_schd/f
Restarted the http-server and webcache: no result.
Configured the same apex on another application server, pointing to the same database: no result.
Allright, database alert-file shows:
ORA-07445: exception encountered: core dump [opidsa()+386] [SIGSEGV] [Address not mapped to object] [0x000000000]  
There were no changes (really, there weren’t…) in the past few days.
Points out to be a bug in 10.2.0.3 (with any version of Apex): bugnr 5745817 :
“Implementing regular flushes of the shared pool can prevent the problem from occurring.
The problem is fixed in 11g via non-published bug:5648872 and the fix is included in 10.2.0.4.” (note 418531.1)
The patch is also available: 5648872
For the time being, ‘alter system flush shared_pool’ is fine for me, until we upgrade to 10.2.0.4 (or 11gr2 of course… :-) ).