Do you get the tabcmd error code 16, Invalid username or password?
A cause of this error is having a special character in the password.
For example, Tableau interprets %1 as a parameter. To resolve this use an escape character. In the command line write %1 as %%1. The preceding % acts as an escape character.
Another special character Tableau can’t interpret is # (the hash symbol or pound sign for any Americans).
I was unable to find an escape character for the hash symbol.
Therefore I had to change the password, removing the #, to make tabcmd work.
If anyone knows better ways around this than changing the password please write in the comments.