If the error is issued in MD62, check t-code SM12 and see if any user is locking the requirement on table PBIM.
If the error occurs in BAPI BAPI_REQUIREMENTS_CHANGE, or BAPI_REQUIREMENTS_CREATE, or FM REQUIREMENTS_MAINTAIN, except checking lock entries in SM12, you can also consider implementing the user exit EXIT_SAPLM60E_001. Here you can call the function module "ENQUEUE_EPBIM" to try to lock PBIM data. If it fails which means a lock exists, you can then use FM “ENQUEUE_READ” read the lock information and write it to your own tables. In this way you can check later which user /transaction was locking the PIRs. If PIRs can be locked in EXIT_SAPLM60E_001, you can then use function module "DEQUEUE_EPBIM" to unlock them so that PIRs can be processed later.
If the error occurs when transferring requirements from APO to ERP, check if the SAP Note 1906918 is implemented on your system. Also make sure that in release activity there is only one action of R/3 Transfer profile.
Related SAP Notes and KBAs
1906918 - DP job with overlapping selections processes some combinations twice