To profile different aspects of your application, the Performance profiler includes several counters. All of the counters, except for Elapsed Time, use a special driver for their work. Only one counter can be running on your computer at a time. AQTime displays this message when you are trying to start profiling with a counter that uses the driver, but the driver is already being used by another counter which is running in another instance of AQTime. You can start profiling after this counter stops using the driver.