Hi Josette. I had this happen to me also about three forum versions back. I think it only happened to me when I'd access the forum and had unopened IMs. I'd get a pop-up notification telling me I had unopened IM messages, "Would you like to see them" (or something like that), and then I'd get a pop up window telling me I should download software so that I could take full advantage of "whatever". When I'd try to download the apple version of whatever they were suggesting I needed, I was not able to download it. I was never able to rid myself of the problem. Then the forum changed to a new host (or whatever, sorry I'm not good with the computer lingo) and the problem went away. Sorry to use so much space to not really help you, but I wanted you to know that at least someone else had the same problem.
Hope you are able to solve the problem,
dom