v2.2.24 structural object class modification not allowed

[Curt Blank <curt@uwm.edu>]

Got this when trying to add a user to our Calendar application that 
writes to LDAP:

Apr 28 14:37:19 ldap01 slapd[31502]: entry failed schema check: 
structural object class modification from 'uwmPerson' to 'ctCalUser' not 
allowed
Apr 28 14:37:19 ldap01 slapd[31502]: conn=155 op=5 RESULT tag=103 err=69 
text=structural object class modification from 'uwmPerson to 'ctCalUser' 
not allowed

Now my question is, is this modification not allowed because I have not 
allowed the Calendar application write access to the 
structuralObjectClass attribute, or is it not allowed period?

Obviously new users have this set to uwmPerson when they are added to 
LDAP and when added to Calendar this needs to change to ctCalUser 
because the ctCalUser objectclass has SUP uwmPerson STRUCTURAL in it.