Diagnosis
You want to work on the BOM for material &V1&. One of the followingsituations triggered this error message:
Your are already working on the material master in another session.
The material master is currently being processed by user &V2&.
The material master has just finished being processed, but the systemhas not posted it yet.

Procedure
Try to access the BOM for this material later.
If the BOM is locked over a long period of time, ask user &V2& why itis locked.