I'd ask for explanation of this error which I don't understand:
Cannot generate timetable, because for activity with id==312 you have no allowed preferred room (from preferred room(s) constraints).
I guess there are at 2 or more conflicting room constraints referring to the same activity.
For example a room constraint for subjects and and other room constraints for activity tags. FET try to care about both but it is impossible in your sample.
Go to FET -> Data -> Activities and select activity id 312.
Check the information about at the right side (if you use a left to right language). You can see the room constraints there. Maybe you already understand then why it is impossible.
please attach your file if you can't find the problem.
I've solved this. I haven't added the room for subject allowed rooms. Thanks.