It may sound silly for me to say this, but I need to upgrade to Oracle APEX 4.2.1 from Application Express 4.0.2
How to upgrade from 4.0.2 to 4.2.1
I searched through forum but didn't find problem specific solution ... please help
i would recommend to read the installation documentation, section "Upgrading from a previous version of Oracle Application Express".
Some two years back I too experienced the same problem. Excelent Guys on this forum helped mee. I am sorry for those who helped mee step by step because I had forgotton to mark that thread correct. Now I mark it correct.
See the thread Unable to upgrade Apex 4.0
What I did on my laptop
Here's some further info from when I patched to 4.2.1