Backup Error After Upgrading to 12.5

[testttt]

We upgraded Plesk 12.0 to 12.5. Before upgrade we were backuping succesfully every week. After upgrade we get errors while automatic backup in both full and incremental backups. It gives errors:

ERROR: (server object 'server') Error in execute 'backup_encrypt' ' --encrypt-by-plesk -backup-files-map "C:\Program Files (x86)\Parallels\Plesk\PrivateTemp\tmp56736.tmp"':
Source file is not accessible.

ERROR: () Error in execute 'backup_encrypt' ' --encrypt-by-plesk -backup-files-map "C:\Program Files (x86)\Parallels\Plesk\PrivateTemp\tmp56736.tmp"':
Source file is not accessible.
​

How can we solve this problem?

 

[testttt]

When I enter to Backup Manager page, It says above "3.11.2015 03:30 backup created, but some problems occured and backup may not be valid" (I translated it from Turkish)

There were green ticks at left sides of old backups. But in new backup records there are gray rounds at left sides. And when onmouseover it says: "
This is not valid backup. Files can not be restore from this file. Click backup name for details." (Translated from Turkish)

When I click on backup name it redirects to main page of Plesk Management Panel and gives this error on above:
"Error: [Errno 2] No such file or directory: u'C:\\Program Files (x86)\\Parallels\\Plesk\\Backup\\clients\\D\xddNCAY_SU\\backup_info_1510260330.xml'"