Apex, HTTP-404 while clicking ‘application builder’

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