it happened to me too, but it is nothing to worry about.
You see, Photobucket, let you have some limited space AND limited bandwidth for free.
Now, your post is viewed by a lot of people, and if your picture are looked at very much (thus becoming very popular in their terms) the generate a lot of traffic and you exceed the bandwidth they let you use for free. Fortunately, this situation ends with the turn of the month when the bandwidth counter will be resetted.
No use in deleting old images as I did too

as this will free space but not bandwidth and you will have to restore them if you want them to appear again in your posts.
Hope this helps.
ciao
Edo