Can't assign roles to membership types, various errors

Hi, I would like to make a community website with membership types and give them special rights. I thought that the easiest way of doing this would be of assigning WP roles to membership types. But I can't as I get error messages.
I also had a lot of errors when activating the simulation mode, making my back-end completely inaccessible. I found a way to reset the access, but the simulation mode is still problematic.
Can somebody help?