You'll need to make sure the ACL is setup correctly in stconf.nsf to make sure users can schedule meetings. Can users use the test meeting function?
I've had issues where the ACL of the stconf.nsf gets corrupt and have had to remove and readd groups before getting it to work again.
To see if there's an issue w/ LDAP consider changing the default access of stconf.nsf to author. If it works, then maybe group lookups are not working.