The Android Virtual Device 'myEmulator' is currently running an emulator and cannot be deleted.
I did delete all the avd process that were running on my Mac OS X but still the error persisted. (check if avd is running through Activity Monitor on Mac or Task Manager on Windows)
To resolve this issue you need to locate .android folder on your HDD. The location for .android folder is different depending on what Operating System you have.
Mac OS X/ Linux/ UNIX
1. Go to terminal.
2. Goto root by typing : cd \
3. Goto Users/
4. Now type : cd .android
5. Now type : cd avd
You would see directories with emulator names. Delete all those emulator's (.ini and .avd) files from here that you do not want.
Alternate way : You need to unhide hidden folders on your Mac OS X to see .android folder. ( how to see hidden folders on Mac OS X : link )
Goto Users Directory where Android Eclipse software has been installed. Now look for a hidden .android directory. Get into avd dir and delete the file and folder that have your emulator name.
Go-to AVD Manager and refresh and you would see that the AVD is been deleted.
Windows XP, Vista, 7, 8
For Windows Operating system you will find .android folder under C:/Documents and Settings/
This can be C:/Users/.android if you are running Windows 7 or Windows 8
Now look for avd folder and delete all folders and files (.ini files) that has the name of the avd you do not want.
Hope it helps!