Glad to know I'm not the only one. This just happened to me while I was not opting in any current betas, I attempted to opt into a beta with no luck. I reinstalled Steam, but to no avail. I tried running GE:S vanilla, assuming it could've been a problem with my reskins, gamemodes, or sprays, but that didn't do anything (luckily I backed them all up). I even tried reinstalling GoldenEye: Source but I hadn't struck any gold.
I connected to a Counter-Strike: Source server to see if this problem was throughout Source MP, but CS:S worked like a charm. This is especially annoying since I was just about to test my custom sprays and rent out a GE:S server. This is the first time this has ever happened to me, and I could easily believe this is on Valve's end which makes me hope they fix this soon.
EDIT: Rediscovered this old post while conducting a routine security check-up. Yes, it is important to fix typos 7 years after the fact. No, I will not fix the sense of uncertainty implied by my expression ("I could easily believe") with respect to who was at fault with this when it was obviously a Valve Software issue – to that extent I feel it wouldn't be proper to alter my previous statements.