So I've managed to lose ED-E somewhere in/near Vault 11. I have the latest patch for the 360 and so it shows ED-E as being pretty much right on top of the Vault 11 icon on the World Map. However, when I go to Vault 11 and go inside, ED-E is nowhere to be found. I've scoured every single inch of the vault no less than 3 times, walked around the outside of the vault at least 5 times (getting killed by a freaked-out Nightkin on at least one occasion). I know I'm not unique in having lost a companion, I just wonder if ED-E happens to get lost or stuck in a specific place in Vault 11 that I'm just missing. I haven't found anything on the interwebz but was hoping that someone had gotten lucky and found that little bucket of bolts somewhere specific in or around Vault 11 and could help me out.
Thanks for any help!

Yeah, ED-E's spontaneous disappearances are old news.

I had the exact same problem with the exact same vault....I got Dead Money and when I entered there it told me he than returned to primm but that was the only way I could get him to get unstuck from that vault....Of course once I completed dead money and went to Primm I never saw him and the Lucky 38 always registered that I had a guest with me still even if I was alone I was than able to get Rex and procede otherwise like Ed-E wasnt with me anymore.

In addition I dont know if it's the game glitched up at the Lucky 38 thinking Ed-E is still with me but since he got glitched in Vault 11 I have not been able to go back to my suite in Lucky 38 unless I kill Victor, therefore losing the quest, The House Always Wins I. I think you can bypass this by accepting the Legions invite though and going to the bunker under their camp because there Mr. House will appear and The House Always Wins quest is added but I dont know if it's for part 1 or part 2 and also dont know if the acheivement will pop that way when it's completed. I am starting to work on that now though and can let you know.