I frequently encountered the below error:
emulator: ERROR: the user data image is used by another emulator. aborting
Once I get this error, I typically restart the emulator and that works most of the times. Sometimes I have to do wipe data for it to start connecting. However searching on google, returned me this link:
The easiest solution that worked for me is to invoke the command below. Best part is you need not restart the emulator,
adb kill-server && adb start-server
adb executable is part of the tools in your android sdk.