Hi Akshay
Check for any custom table is created in this custom user exit where it allows only particular user and excludes all other user as per the entry in that table which is defined in the custom user exit.I would suggest goto transaction SE91 and check the code and click for where used and check for authority check also.
If you not sure about this then involve your developer in this code check he/she will be able to tell you what checks are performed when the t-code is executed.
Regards
Pradeep