Hi Naveen,
As Chandu said, you need to be specific while providing the authorisations in the authorisation object C_DRAD_OBJ. This object contains 4 authorisation field values
1) ACTVT(Activity) which allows creation/change/delete of object link from the DIR
2) DOKOB(Linked SAP Object) - In combination with activity you can assign specific objects like MARA,PRPS etc. to user
3) STATUS: In combination of above 2, you can also restrict using specific status i.e. only in 'CR-Created" status user can change/delete the object link.
4) DOKAR: The user is allowed to create/change...object links in which all document types.
If you have already specified all these above, then the user is getting other object links authorisations through some other role. Check with SUIM tcode for details.
Regards,
Ravi