Nothing bro, that is issue with permission of files. After changing permissions everything fine,  but it was changing permissions automatically after opening file or edit. 

@Ghany
So how did you fix it?

you need to install osclass again with the old database

Sorry for delay,

nohing to fix that bro, this issue was causing only because  permissions

0755 for print ad plugin folder
index.php and print.php need to have 0644

thats it

755 also for the whole plugins folder, problem solved. Thanks Ghany! 

I made 755 permission on the folder and files of the plugin print_ad and still giving the server error message, what do I do now? I have no more ideas!

@paulinoromeira
There were recenlty about 5 people that were blaming us how bad are our plugins and how bad is our support because of this error. Everytime problem was on hosting side, so I am not going to explain again what you can do. It is described here, just read.

@paulinoromeira
contact your hosting provider they will solve, this is only a matter of permissions

I contacted my server and correct the permissions change, thanks