The error message you see may vary as I find that other text tends to overlap the error message such as this which was displayed on one of our servers when you hit the ALT+F11 key from the main ESXi screen:
If you see this message, you’ll need to poke around the BIOS and depending on the type of server, look for a feature that is similar to:
No Execute Memory Protection
… and then set it to Enable. Here’s an example of what it looks like on an HP ProLiant DL380 G5:
Press F9 during the POST screen to get into the BIOS:
Select: Advanced Options:
Select: Processor Options..:
Select: No-Execute Memory Protection:
Notice how the bottom box says Disabled? We need to change that to Enabled so it displays the box as such:
There isn’t an F10 option for HP’s BIOS so hit ESC a few times to exit the BIOS.
Now when you reboot ESXi and hit ALT+F11 after all the server completes the boot up process, you should no longer see that message:
I won’t go into the details as to what this function does because I would not do as good as a job than other websites so here’s a link to Wikipedia that would get you started: http://en.wikipedia.org/wiki/NX_bit.