A user of mine, using Tableau Desktop, was getting an occasional error message sent by the SQL Server data source stating a "...parallel queries..." issue during a live connection. After investigating what was happening, the SQL Server dba determined it was due to parallelization by the db. The default setting is zero, so the db will use as many processes as are available for breaking down and thus processing a submitted query. When another query comes along it gets the cold shoulder and an error message is generated. Changing the default setting to a reasonable value (determined by the dba) other than zero fixed the issue for us.