Unable To Login To Oracle Applications After Upgrading from 11.5.10.2 to R12 Or After Cloning

After the process of upgrading from 11.5.10.2 to R12 through executing the "Finish the Upgrade" , got the error : 

"Login Page" failed during the "Validate System Configuration". 

When t

rying to login via http://.:webport/OA_HTML/AppsLogin got :

"The page cannot be displayed" error message

ERROR
"login page" failed
.

Cause

The problem is caused by incomplete or malformed configuration files during the upgrade.

Solution

To implement the solution, please execute the following steps:

1. Cleanup the malformed configuration/setup files by running:

EXEC FND_CONC_CLONE.SETUP_CLEAN;
commit;
exit

2. Regenerate all configuration files by running autoconfig.

3. Delete all files under $COMMON_TOP/_pages.

4. Recompile the jsp's by running :

$FND_TOP/patch/115/bin/ojspCompile.pl --compile --flush -p 2

5. Start the Apache service.