Try troubleshooting something easier first. Install tabcmd on your local machine, and try doing tabcmd login to make sure that works. Then play (carefully) with some of the other commands like runschedule.
Tabcmd does not need to be installed on your SQL Server. But since I assume you are triggering the schedule based on events happening in SQL Server, this might be easier to manage if you make the TabCMD call a step in a SQL Agent Job or an SSIS package, or somesuch. For a while we did this, then switched to calling a scheduled task on Tableau Server because we got tired of updating TabCMD on the SQL Server all the time. Then we moved to a model where we "pull" the appropriate times to run the schedules by querying SQL Server from a script on the Tableau Server machine--that way, all those scripts were managed by the Tableau Server team rather than the DBAs, and it removed any dependencies SQL Server ETL had on Tableau Server.