If you are running Application Express, there is a new patch available. Lots of fixes which you can read about here
I just downloaded patch 25341386 and followed the installation instructions and it went through with no problems at all in just a few minutes.
Verifying Application Express version...
...have version 5.1.0.00.45
PL/SQL procedure successfully completed.
Verifying Application Express version...
...have version 5.1.0.00.45
PL/SQL procedure successfully completed.
PL/SQL procedure successfully completed.
Session altered.
Stopping and disabling APEX jobs
PL/SQL procedure successfully completed.
PL/SQL procedure successfully completed.
Session altered.
Grant succeeded.
Verifying Application Express version...
...have version 5.1.0.00.45
PL/SQL procedure successfully completed.
PL/SQL procedure successfully completed.
Session altered.
...
...
...
Validating Application Express
(09:02:38) Starting validate_apex for APEX_050100
(09:02:41) Checking missing sys privileges
(09:02:41) Recompiling
(09:02:42) Checking for objects that are still invalid
(09:02:42) Key object existence check
(09:02:42) Setting DBMS Registry for APEX to valid
(09:02:42) Exiting validate_apex
PL/SQL procedure successfully completed.
PL/SQL procedure successfully completed.
PL/SQL procedure successfully completed.
timing for: Complete Patch
Elapsed: 00:02:33.76
Enjoy !