How to unregister R12 while OID is corrupted

If OID is corrupted and you want to forcefully deregister OID from R12, run the following command.
$FND_TOP/bin/txkrun.pl -script=SetSSOReg -removereferences=yes



Please check the following section in doc "Registering Oracle E-Business Suite Release 12 with Oracle Internet Directory 11gR1 and Single Sign-On [ID 1370938.1]".

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SSO and OID Registration stores a set of preferences in the Oracle E-Business Suite Database. If the Oracle E-Business Suite Instance is cloned from an existing SSO/OID registered Oracle E-Business Suite Instance, the cloned environment has the same preferences as the source environment and throws errors during SSO/OID Registration. The following command should be called in the post cloning phase or before proceeding with SSO/OID Registration to remove all the preferences or settings from cloned environments.

4.1 Interactive Mode

$FND_TOP/bin/txkrun.pl -script=SetSSOReg -removereferences=yes

It prompts for required arguments as follows:

Enter the Oracle E-Business Suite apps database user password ? APPS
It does the following:

It validates the arguments
It removes the Oracle Home Instance preferences, SSO Preferences and Site level profiles, and OID preferences from the Oracle E-Business Suite Database.
4.2. Non Interactive Mode

$FND_TOP/bin/txkrun.pl -script=SetSSOReg -removereferences=yes -appspass=APPS
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Please note, after dergistering R12 from OID, if you try to register again with the same OID or different OID, the login page may not come though there will not be any error. this is because some config parameter related to SSO are still stored in R12 that is pointing to old OID. To resolve this you need to run proper unregistration once with a working OID.
For again reregistering do the following after forceful deregister.
 a. register R12 with a working OID
b. properly unregister the R12 [not by forceful unregister process shown above]
c. again register OID with R12. Now there'll be no problem