you used up your monthly quota for bandwidth in your account.. thats what most likely happened.
This has happened to me at least three times in the past few months, Barfy. You need to wait until your join date on photo bucket passes, and then they'll give you more bandwidth for the following month.
They started this as a means to motivate people to pay for thier service. If you have several photos up at the same time and tons of people see them on Micechat, your bandwidth will go over their new limit. But it will reset once a month and you'll see your photos again.
I ended up opening an account on Flikr, which has run faster than photobucket for me so far. The downside with Flikr is that once you pass 200 photos, they begin to disappear on the other end. They will still be visible in your posts, but you can't access them from opening your photo page.
In order to see how much bandwidth you are using, go to the very TOP of the page in your photobucket account and look for "account options." Click on it and it should tell you how much you are over and when it should reset. (Your reset date will be under "Member since...." )