Whenever you have GROWLr open it will continously attempt to use GPS to determine your current location. If your phone cannot connect to GPS it will attempt to determine your current location by cell tower triangulation.
First try force closing GROWLr and rebooting your device.
If this does not work, follow the directions below.
Go into your device settings, and find your location services. Tap them to turn them off for a moment, then turn them back on.