When I trid to open GNS 3 to do some network lab. the following error message popped up:

server error [-3200] : unable to create vm instance ‘ghost’ an emulator instance (pid 5640) is already running with identifier 0. if this is not the case, please erase file “c7200_i0_lock”. vm ghost: unable to create instance!

I was attracted by the Keywords”emulator instance”, on my machine, there was a couple of emulator software, one is XAMPP, the others include VMware, Virtual box. But the XAMPP is started by the system on startup. So, I open the Windows task manager and Checked the PID. Although 5640 is not running, but there is one really closed to it, 5644. I think the 5640 is reserved for some sub function of the software, So GNS can’t use it now.

To test my theory, I open the XAMPP control panel, turned off all the services. Then reopen GNS3, and everything work fine now.