We recently found a SalesLogix Mobile Client that would not complete the full data synchronization.  In the Mobile Administrator we found this line under the critical errors: 'Error in SynchronizaitonJob - job has been canceled - invalid column name - 'OPPCOMPETITORID'.  When we looked in the SalesLogix database they had restored the OPPCOMPETITORID was indeed missing.  Our solution was to open the SalesLogix DB Manager and add the OPPCOMPETITORID  field to the Opportunity_Competitor table as a SalesLogixID field.  We mimicked the settings of another SalesLogixID field and had the system syncing in no time.