[@robkk Moderator 11 years ago]

Can you assign topic tags in a regular forum?
Can you assign topic tags in a group forum?
Have you tried creating custom roles?
Have you installed a user role editing plugin?
Have you ran any repair tools in Tools > Forums yet, especially the Remap existing users to default forum roles one?

Have you tried most of the basic troubleshooting steps already?

Troubleshooting