A PST has a policy applied but is failing to process stating an error occurred during processing. In the PST Enterprise Client tracing you can see the following error:
29 13:29:15 388599 BMAProcessor::ArchiveMessageToBMA: SaveChanges failed hr=0x8004060c
The PST file is an legacy format PST which has a maximum size limit of 2GB. Some policies require additional data to be tagged to each message (for example, Copy to Message Archiver policies). If the PST is at its maximum size limit, this tagging fails and the policy cannot be actioned.
You will need to move some data from the PST file to another PST file, or delete data that's no longer required.