Calendar Profile
To add on to what Oscar stated, if the
issue is reproducing for all of your users, look for any field that is
being set by default either through the template or policy. Most
commonly, these type of errors are seen with signatures. So, even if you
blow away the calendar profile, the problem may come back after a client
restart given how the value is being set. If that is the case, you'll
need to isolate which value may be causing the problem.