Message type: E = Error
Message class:  TAX_EXEMPT - Message class for tax exempt certificate 
Message number: 021
Message text: Error in enqueue! Tax exemption &1 can not be locked
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The SAP error message TAX_EXEMPT021 indicates that there is an issue with locking a tax exemption record in the system. This error typically occurs when there is an attempt to access or modify a tax exemption record that is already locked by another user or process. Here’s a breakdown of the cause, potential solutions, and related information: Cause Record Locking: The tax exemption record you are trying to access is currently locked by another user or transaction. This can happen if another user is editing the same record or if a previous transaction did not release the lock properly. System Issues: There may be underlying issues with the enqueue mechanism in SAP, which is responsible for managing locks on records. Long-running Transactions: If a transaction takes too long to complete, it may hold onto the lock longer than expected, causing other transactions to fail when trying to access the same record. Solutions Check for Active Sessions:
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