As it is possible to run keyword tests from other keyword tests (see the "Run Keyword Test Operation" help topic ( http://www.automatedqa.com/support/viewarticle.aspx?aid=3100 ) for more information), I recommend that you create a "master" test which will launch your other tests multiple times in a row and change the parameters as needed.
The message is posted because only a single instance of the tested application is supposed to be launched according to the Count property of the corresponding tested application. This is the default value, and I strongly recommend that you do not increase it, as it may cause problems with objects recognition. I recommend that you use the WaitProcess method (see the "WaitProcess Method" help topic ( http://www.automatedqa.com/support/viewarticle.aspx?aid=6090 ) for more information) to check whether an instance of your application already exists in the system and close the process if the instance of your application is found before the new instance is launched. Since your application will be restarted in this case, this can also increase the stability of your tests, as the application will be returned to its initial state.