long time & important http address is being blocked all of a sudden

I cannot figure out why this important site which I have used for years is suddenly being blocked. the message I'm getting says-"Firefox has detect that the server is redirection the requested address in a way that will never complete. This problem can sometimes be caused by disabling or refusing cookies." I don't believe I have made any changes to cookies or anything else in the past few days so I don't know what to fix. Please help Choochum Mavin thanks