I am facing a peculiar but annoying problem. I have Update 6 and both the DLC's installed. I have completed all the Quests in Fallout New Vegas (Barring the Last Storyline Quest and "For Auld Lang Syne" and also "Dead Money" DLC. However, upon returning to the Mojave after finishing Dead Money, when I want to recruit Arcade Gannon from the Lucky 38 casino in order to complete "For Auld Lang Syne", I am unable to recruit him. Whenever I have Ed-E or Rex (the non-human companions) there is no dialogue option to hire him. If I fire them and I have nobody with me, even than he says that I already have a companion and the game also prompts that, although I don't have any. I have tried several methods like resetting him from the console, tried firing Ed-E and Rex, hiring only Rex, Firing all the other companions and telling them to return to their bases and re-entering the casino, loading previous saves, going to Vault 22 and repairing the elevator, spending more than 72 hrs in the game but nothing has helped. I am desperate to play this only secondary mission left in the game. If anyone has faced a similar problem and could help me with some tips, It would be greatly appreciated. Thanks in advance.

I had this happen. Turned out he just didn't like that i was helping the NCR. Soon as i stopped helping the NCR and started doing the wild card he would join me again.
Or i could be wrong and its a glitch and it'll work it self out?

OK, Finally its fixed. After hours of searching on the internet, i downloaded a custom made script from here:
http://www.newvegasnexus.com/downloads/file.php?id=38355
After downloading I extracted it and copied the file to the Data folder inside the Fallout New Vegas Folder (For example in my case as I had installed the game in D:, I pasted the file in D:/Fallout New Vegas/Data, after which I started the Fallout Launcher, clicked on data files, enabled the script be checking it, launched the game, hired Rex/Ed=E (any 1) as my companion, approached Arcade at Lucky 38 and the dialogue option was there and I was able to hire him and do his quest. I am very grateful to the author of this script: Stygs, all credits go to him. Hope this will help anyone facing the problem I faced. Cheers to WOODBaron for replying.