Oracle Message ORA-12832 - Could not allocate slaves on all specified instances

ERRORCould not allocate slaves on all specified instances
CAUSEAfter executing a query on a global v$ fixed view, one or more instances failed to allocate a slave to process query
ACTIONTo allow results to be returned by sucessfully allocated slaves, execute ALTER SESSION SET ALLOW_PARTIAL_SN_RESULTS=TRUE statement, or check parameters of instances