Hi,
The problem is that your test has an operation or calls a method that runs the browser. As your browser is already running, TestComplete cannot launch one more browser instance and displays this message. This is done to prevent situations when you record or perform test actions against multiple instances of an application and therefore get incorrect results.
To resolve the problem, delete the operation or method that runs the browser from your test. Also, before the test run, make sure that you launch the browser and TestComplete under the same account.