Thank you very much for your help, it's much appreciated. However, what I don't understand is when it wouldn't upload, the first thing I did was go to PHP configurations and changed the "upload_max_file size" to 20M, which it is still on now because I have just checked. I've experienced problems with uploading large files before and I've always got around it by changing this value. However, I've also managed to upload direct from the URL in extension manager as well, this is something I could get to work either. Anyway, very strange. Why I couldn't get it to work.
Thanks very much, and if you have any thoughts on this, please let me know.