I'll try to keep this simple and not to complex for none tech savvy users. Shadowkeep doesn't support particular unicode characters, and thus doesn't know how to deal with them if put in a clans motto, callsign, and/or name, resulting in a 'WEASEL' error. A temporary fix while bungie adds support back would be to removed offending unicode. If you aren't sure what classifies as such, remove anything that cant generally be typed on a keyboard. Safe to say only use letters and numbers that can be typed on an English based keyboard. Update: please check if you have an invite to a clan, if so decline it and see if it works.