after i had an exchange with the online support i was asked to report my issue here.
In backend i get the same error everytime i try to make changes in shop section or setting section :
Linux host1 3.16.0-4-amd64 #1 SMP Debian 3.16.39-1+deb8u1 (2017-02-22) x86_64
Joomla! 3.6.5 Stable [ Noether ] 1-December-2016 22:46 GMT