ESXi 5.1 Upgrade – No eXecute (NX) bit is not enabled on the host

I was trying to upgrade a ESXi 4.1 host to ESXi 5.1 and got the below warning message after a scan.

No eXecute (NX) bit is not enabled on the host.  New ESXi version requires a CPU with NX/XD bit supported and enabled.

The warning about the Dell OpenManage software module does not prevent the upgrade but the NX bit warning does.

Fortunately, my Dell PowerEdge 2950 does support NX but it was disabled by default.

Enable the Execute Disable option in the BIOS and it solved the upgrade issue.