Hi hexa , thanks for replying ,
actually i did setup the forum before on another hosting provider but I want to use 000webhost ,
so tried to setup the forum on 000webhost & then the error occured.
I think the issue is not related to the forum, it seems to be related to 000webhost , may be one of the default settings of my 000webhost cpanel that need to be changed ! I don't know how to solve this issue
I also tried to upload the files again but nothing solved !