Function not available to this responsibility When Trying to Access Custom Form

We cloned R12 instance in test server after that the Apps technical team faced
 'Function not available to this responsibility' error when they trying to access custom form.
The reason for this issue is that, missing entry for CUSTOM_TOP under default.env file.
Then we followed below steps to solve this issue:
    1. Login to Linux server with APPLTEST user.
    2. Go to $INST_TOP/ora/10.1.2/forms/server directory.
    3. Ensure that your CUSTOM_TOP's are registered in the default.env file.
        We should create an entry for env variable CUSTOM_TOP
        like below in default.env file present under location.
        $INST_TOP/ora/10.1.2/forms/server directory.
For Example:
APPL_TOP=/home/applmgr/PROD/apps/apps_st/appl
CUSTOM_TOP=/home/applmgr/PROD/apps/apps_st/custom
     4. Restart the middle tier services.
     5. Retest the issue.