When attempting to connect to DataGate, a user may encounter an unhandled exception accompanied with the detail "QUSCRTUQ create user queue OS/400 api failure"

When a user connects , the IBM i attempts to allocates an amouint of disk space to create the user space.  If for some reason ( low disk space or the user profile has reached their storage limit, this error will be the result) 

More than likely the user profile has reached its storage limit.  You'll need to work with the IBM i administrator to either increate the storage limit for the user profile , or remove existing objects that belong to that profile.  (Or set the storage limit for the user profile to *NOMAX)