You have assigned a copy policy to a PST but it fails with the error 'There was a problem preparing items for upload to the agent'. In the PST Enterprise Client tracing you can see:
23 17:31:06 PSTMoveIterator::FoundMessage - Processing message with subject 'My email message'
23 17:31:06 PSTMoveIterator::AddPreUploadProps() - Message GUID SaveChanges() failed. hr=0x80070005
23 17:31:06 PSTMoveIterator::FoundMessage() - This message failed so disallowing completion of the PST
In order to keep track of which items have been copied from a PST file already (and thus avoid data duplication), an additional property is added to the original item in a PST to prevent it from being copied again. In this case MAPI error 0x80070005 MAPI_E_NO_ACCESS is returned. The indicates that the user has insufficient permissions to modify PST data.
You may have applied a restriction in regards to creating or modifying PST data to the affected user via Group Policy, or another configuration method. You will need to remove this restriction so that PST Enterprise is able to process the user's PST data.