Are u running with Debug mode or Release mode?
If running in Debug mode you may need to stop the debugger first.
Everyonce in a while I need to remove all versions of my app on the phone / emulator.
You could also try to disonnct the bridge first.
I feel that sometimes these crashes or test runs or emulators build up to where I can't get the phone to work/connect.
So I just reboot both the phone and the pc.
Other times I'll check the windows taks manager and have 6 or 7 adb.exe running.
I'll exit b4a, wait a few seconds, then end proceess the remaining adb.exe processes.
Then start b4a again.
hth