Okay, so here's what has happened twice in a row now, to the best of my recollection. Apologies if this is a known thing, a quick scan of the topics didn't show the exact set of circumstances but then it could well fall under known bug/freeze issues.

Anyway, here goes:

1) Outside Crimson Caravans, I tell Cass and Rex to follow me.
2) Open Pip-Boy and fast travel to Mojave Outpost
3) Spot a trader, and think "ah, good time to buy and sell"
4) See a whole bunch of caravan cards, select them to buy and then hit square to complete the purchase
5) Console lock up. No buttons seem to work, holding the PS Button gets no Quit option, pressing it doesn't bring up XMB etc
6) Give it all of 10 seconds before thinking "maybe this is the 'playing for too long' freeze, I best restart the PS3"

So I restart it, jump into Fallout, load the autosave which is outside Crimson Caravans (I guess it didn't autosave in Mojave Outpost) and try again.

1) Outside Crimson Caravans, I tell Cass and Rex to follow me.
2) Open Pip-Boy and fast travel to Mojave Outpost
3) Spot a trader, and think "ah, good time to buy and sell"
4) Select just three Caravan cards, a grand total of 9 caps in cost and hit square to buy them.
5) Console lock up. Same problem.

So, at the initial, unscientific glance, I cannot buy anything from this caravan trader and his Brahmin. I haven't let it wait for a few minutes say, so I don't know if it's just a long freeze, but it does seem like a lock up with no option to force quit the game through the XMB. Whether this is because I fast traveled, it was still autosaving, or something like that that I don't yet know, I have no idea. Suffice it to say I'm not yet buying or selling anything from that trader under I know more about the situation.

It might be a simple fix (like don't rush up to him, save first), or it might be a rather annoying, game freezing, console locking up bug. Which would svck. Having spent a lot of time in Fallout 3, even through the extremely freezey DLC, I'm used to Fallout having problems - just not ones that prove this problematic. Any ideas from anyone here?

I have the same problem with the Mojave Outpost trader, I have tried fast traveliing in from different places, using the trader and repairer in the base etc before trying again and every time it freezes up. I haven't tried not buying the cards from him which may be causing the freeze so that will be my next try.