Files were skipped in backup

Hi ,

i'm taking a backup from Linux server. every time i'm getting the backup scheduled success message with error notification that" However, the following conditions were encountered: 45 files were skipped." .

in details in backup log mentioned as below. it's mentioned for all of 45 files.

"Unable to open the item \\192.168.1.20\[ROOT]/deb01/app/oracdsl/oradata/dbcdsl/tr01.dbf - skipped."

please advise me.