Do you have QTP setup (options turned on) to accept remote run commands from QC? There are a couple of things you have to turn "ON" in QTP to allow QC/TD to call it and run a script. Check the help on QTP about this.
Choose Tools > Options or click the Options toolbar button . The Options dialog box opens.
Click the Run tab.
Select the Allow other Mercury products to run tests and components check box.
For more information