I removed the emulator and reinstalled it and got the same error.
Emulator: emulator: ERROR: Running multiple emulators with the same AVD is an experimental
Removing the .lock files did the trick for me. Find the avd and remove the lock files. In a Mac .android/avd/'NAMEOFAVD.avd directory . The files I removed were hardware-qemu.ini.lock and multiinstance.lock.
.android/avd/'NAMEOFAVD.avd directory
hardware-qemu.ini.lock
multiinstance.lock