What does a 'Result = -15' mean from the MSSCCI RTC / Rhapsody integration when attempting to get the CM status of a Rhapsody Model file

 I have a user that is utilizing the RTC MSSCCI plugin inside Rhapsody.  We are using RTC 6.0.3 with Rhapsody 8.2.  We have configured their stream to make most Rhapsody files read-only when loaded, requiring users to obtain a lock (check out in the MSSCCI interface) to make the file modifiable.  My user just reported an issue where she is receiving a 'Result = -15' output when attempting to refresh the CM status of her Rhapsody Model.  She has other models in this component that are showing their status fine.  I have tried searching for this return code, but have not found any public sources of information.