Oracle Apps R12 Forms Not Opening

The forms for Oracle Apps EBS may not open for many reasons. Follow below steps to find out:-
For a particular Form:-
Most of the time its related to some database objects or the particular form executable.
a. Compile all ( Mainly Apps owned ) db objects.
b. Compile particular form executable.
For All forms.
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1. Always check the DB, and alert log.
2. Check file system space.
3. Check Apache and Forms log.
$LOG_HOME/10.1.3/Apache/Apache/logs and $LOG_HOME/10.1.2/forms/logs
4. If you are using R12 with IE8 then check Metalink doc 1069497.1,
Also check 389422.1 for recommended browsers and settings.
5. Check timestamp for files like $AU_TOP/resource/CUSTOM.* ,
this will tell you if someone has modified the pll and then the changes should be reverted back.
6. Try checking the form sessions from your server as below
ps -ef | grep frm
This will show the frmsrv and frmweb processes. If it doesn't then the issue is in spawning form session.
You can check the timestamp for frmsrv/frmweb executable, if this has got changed. You can relink this by below.
a. Source the Application environment
b. from location $ORACLE_HOME/forms/lib
run :- make -f ins_forms.mk install
7. In other case if from sessions are there and you are not able to open the form, then check the direct form login as below.
http://server:port/forms/frmservlet - for servlet mode
http://server:port/OA_HTML/frmservlet - for socket mode
8. If above works then you can go to adadmin and compile jsps, or can have clear cache bounce.
9. If step 6 doesn't work then check for dbc file present at $FND_SECURE.
a. The file should have correct entries for Application Server Id, as it is in FND_NODES table.
b. All the passwords guest,applsyspub etc are ok, or change the guest password using FNDCPASS
c. You can correct the dbc file manually, or regenerate using $COMMON_TOP/admin/install/adgendbc.sh
10. Bounce forms server and retry.