ESXi 5.1 crashing

You're running a very old version of VMware. The build you're on, 799733, is from September 2012. The current build of ESXi 5.1 as of this date is 1612806.

You're supposed to run updates! (why) Reference the VMware patch portal.

Many people don't update or patch their ESXi installations. I don't understand why. But this is leading to a flurry of questions about bugs that have been resolved in later releases.

Your particular issue is fixed in the following VMware patch: PR932615. There appears to be a workaround that would require a reboot, but it's best to just update the host.