Error occurred on checkpoint file

Hi,

We have decided to use our file server as a storage point for our bak-files and have therefore selected the UNC path \\srv01\DB_Backup\ as the backup directory. All bak-files are successfully stored in sub directories of this directory without problems. The problem is though that the event viewer on the db server shows a lot of checkpoint file errors upon every restore operation. The error event id is 18272 and the error message is as follows:

"During restore restart, an I/O error occurred on checkpoint file '\\srv01\DB_Backup\RestoreCheckpointDB16.CKP' (operating system error 5(failed to retrieve text for this error. Reason: 15105)). The statement is proceeding but cannot be restarted. Ensure that a valid storage location exists for the checkpoint file."

Does anybody have an idea what can be causinig these errors? Are the error messages severe? It should not be a permission issue because we have given everyone full control on the directory without any change in result.

Thanks in advance!
Best regards
Lars