the user data image is used by another emulator. aborting

i am creating an simple application and run this application , its w开发者_开发百科ork perfectly but when close my application on emulator and run another time its give me an error like this ,

[2011-09-23 20:17:57 - DatabaseApplication] Android Launch!
[2011-09-23 20:17:57 - DatabaseApplication] adb is running normally.
[2011-09-23 20:17:57 - DatabaseApplication] Performing com.database.DatabaseApplicationActivity activity launch
[2011-09-23 20:17:57 - DatabaseApplication] Automatic Target Mode: launching new emulator with compatible AVD 'Android1.6_API_4'
[2011-09-23 20:17:57 - DatabaseApplication] Launching a new emulator with Virtual Device 'Android1.6_API_4'
[2011-09-23 20:17:57 - Emulator] emulator: ERROR: the user data image is used by another emulator. aborting

I have got the answer of the Question : Problem is solved using following below step :

step-1 : go to c:\user\name_of_user\.android\avd\name_of_avd 
step-2 : delete below folder
         1. userdata-qemu.img.lock
         2. cache.img.lock

Run your application , every thing going right but i don't get right solution , why this problem is generate.

Thank You Rahul Mandaliya