The documentation requests to add the gathering account to the rim_db_admin_audit_sr_helpdesk role. That role no longer exists in BES 5.0.
WORKAROUND
For version BES 5.0 and later the procedure has changed. The Messagestats gathering account must be assigned on the BES Management configuration database (by default BESMgmt) the db_datareader role.
STATUS
Change Request TF00147634 has been raised for the documentation of the MessageStats Report Pack for Blackberry to be amended accordingly