not just you. i'm using firefox. logged out, couldn't log back in. could open with opera. went back to firefox, cleared cookies, logging in and it's fine. I also could not accept a HIT, try for a qualification, etc. Just logged back in now and my available balance no longer says unavailable.
Even, I got the same issue. Also showing the below message : "We have detected that your Amazon Payments account cannot be used with Amazon Mechanical Turk"
nvm mine's reading unavailable again. if that's the case, then i think it's maybe a server issue - and that would explain some/not all having the problem. sometimes the fix is a flip of a switch on their part edited to add: unavailable on chrome and firefox. guess it's time to go write submission texts at other sites since mturk is down atm.
Glad to know I'm not the only one having this problem. At first I thought, "uh oh, but, well, something must be wrong with the server" BUT then I accepted a hit and instead of taking me to the hit it took me back to the dashboard. That really worried me. Oh well, a little more time to do something to the house until they get this figured out!
...be careful with accepting any HITs with a short timer for (I'd guess) an hour? Because mine came back for a few minutes and then went out again. I'd hate for it to go out and not be able to finish/return a HIT