There is no need to click the "add photo" icon above when copying the URL from Photobucket or Tinypic. Just click the the URL address to the right of "IMG" in photobucket Or the window under words "IMG code for Forums or Message Boards," at Tinypic, to copy and paste in the post window of SMF.
I have also been unable to upload attachments for at least the last hour. (I last sucessfully uploaded a JPG on 10/26, but haven't tried since.)
Tonight, I tried PDF, PNG, and JPG with no luck. All were within the board's limits in file size, pixels, etc. In the process of trying, I cleared all my previous attachments in case I was over a total storage limit, but that didn't make a difference either.
I can, however, still link pics using the [ img ] tags without a problem.