So I fired Arcade Gannon to do some other companion quests, and now when I go back to Freeside to hire him so I can take him to confront Benny with me, I can only ask about his "take" on "the situation" and ask him about himself, with no option for me to hire him. The thing is, if I bring Boone with me, I am able to ask Gannon to join me but he says my party is full, and as soon as I fire Boone, the option to hire Gannon disappears, in effect making him unhireable.

I've come across many bugs so far and this is the first one I've been unable to resolve, and it's more than a little frustrating. Has anybody else got this bug, and if so, do they know any ways to get round it?

This exact same thing just happened to me. It's incredibly frustrating- if I can't get his quest it'll totally screw up the endgame. I wish I had some advice. I've tried everything I can: making sure the Legion hates me and the Followers love me, making sure I had no companions waiting in the Lucky 38- I even dismissed ED-E just in case. Nothing worked. I can only assume it's a bad glitch where the game gives you that dialogue because it thinks he's already your companion, so you don't get the option to ask him to BE your companion.
If I hear anything about a fix I'll post it here. Of all the glitches I've run into, this one's the worst.

I have this bug on the PC so I think it might be a scripting problem.

I've just encountered this too. It's very annoying. I tried loading back to an earlier save, and the same thing occured. It may have something to do with encountering the vertibird dialogue with him? That had happened a while ago. I had before then dropped him off and picked him up at the casino multiple times.

Exact same bug here.

I haven't even recruited Arcade yet, though.

I've got ED-E and just finished Boone's armor quest.

I can no longer send companions to the Lucky 38.

I'm having a similar bug with Veronica. I'm never allowed to recruit her, when i've got a companion slot open I can choose the option to travel with her, but when she says something like, "great, shall we get going?" my only possible response to her is something like "No, I can't travel with you at this time"

I found that completing Ring-a-Ding-Ding allowed me to trigger the recruit dialogue again, in addition to firing ED-E. The bug I'm having now though is his quest. For Auld Lang Syne won't trigger. At all. I've visited all the locations that trigger dialogue in him and advanced far enough in the Wild Card quest line for him to give me his quest, but I still have the same dialogue options with him as when I very first recruited him. I think the dialogues I've triggered with him in the past might not "count" because I hadn't got far enough in the story yet, and I don't think I have enough of them left to be able to start over. If that's the case, then his companion quest is broken for me and cannot be started :/

Really getting sick of all the glitches in this game now. It's so much better written and voice acted than Fallout 3, and the story's so much more engrossing, but all the fun is sapped from it because it's so damn broken. I know Fallout 3 was also pretty buggy on release, but not bad enough to entirely spoil the enjoyment of the game. It's good how they're working to patch the bugs but it should never have been released in the first place. What would be better is a public promise that they will in future set realistic release dates and not release them until they have actually been tested.

I finally got so fed up with not having him that I just reverted to the last save I had with him still as my companion (it was like 20 hours back and I had to do vault 34 again, bleah). It took a REALLY long time to get his quest. It happened after I'd completed the Yes Man's second to last quest, as I was walking out of the Lucky 38. Arcade stopped me and initiated the dialogue on his own, I didn't have to ask him anything. I think you have to be far enough in the endgame to have locked yourself to one faction, and you have to have "failed" all the Legion quests by A. choosing any side that's not them and B. being vilified by them. His quest was literally the last thing I did before heading out to Hoover Dam for the final bit, and it happened later in the questline than what's indicated on the wiki, so I think they might be underestimating how far along you have to be before he'll give it to you.

Then again, my game could just be glitched. Or yours could be glitched. Or they're both glitched. At this point I wouldn't be surprised. But yeah, don't give up hope unless the game's actually ENDED without him initiating the quest.

Sorry to hear you couldn't get it working :/ I managed to get the quest in the end, I was on The House Always Wins, VII by the time he talked to me (although I guess that makes sense since the whole point of the quest is to recruit people for the battle). I'm Neutral with NCR and Vilified with Legion, so I think that might affect the quest too.

So I managed to get the quest, finally, and after the quest has concluded and Arcade returns to the bunker to give you his family armour, the dialogue to recruit him is no longer present...exactly the same bug I experienced in the OP.

I am thinking at this point I must have done something to upset someone at Obsidian?

workaround = fire ED-E first and then ask arcade, worked for me

Have that problem too.

Could it be possible that it wasn't a bug that Arcade wouldn't join me after his quest? If the epilogue is to be believed, then he stays with the Followers if you tell him to return to them, or otherwise stays with the Remnant, so either way he leaves the Courier. However, I advised him to stay with the Remnant and I never saw him in the Battle of Hoover Dam, so maybe that's a bug?