When changing permissions via File Manager, Plesk shows an error:
Error: filemng failed: filemng: Error occurred during /bin/chmod command.
This is Plesk internal issue with id #PPPM-3252 . It was fixed in Plesk 12.5 microupdate #2 .
Please install the latest Plesk microupdates.
See KB article # 213943585 for more information about microupdates.