If you take a look at the "event viewer" you con see that tvservice create this error:
Service cannot be started. System.IO.FileNotFoundException: Could not load file or assembly 'Gentle.Framework, Version=1.2.9.18134, etc.
I solved the problem downloading it from mediaportal svn repository in sourceforge site.
it's not installed there by the server installation.. as i don't have MP client installed on the machine i run the server on, and that file is not installed.