I’ve seen this with both the Access Gateway and other Virtual Machines running in XenServer 6.x from time to time. Here is a resolution that worked for me.

1 – “xe vm-list” to get the uuid of the VM that is hung

2 – “list_domains” to list the domain uuid’s so you can determine 

the domain # of the VM above by matching the uuids from this output with the uuid for your VM from the previous command.

3 – “/opt/xensource/debug/destroy_domain -domid XX” where XX is the domain number from the previous command

4 – “xe vm-reboot uuid=XXXX –force” where XXXX is the uuid from the first vm-list command for your VM. (name-label may work but didn’t work this time for me so I used the uuid)

Your VM (should now be) will be back up, and running now. (I use this for my CAG that hang, it’s a nifty way to do it, so you don’t have to reboot the xenserver host)