Don't put a period '.' at the end of an URL.
IE. if someone mentions an URL such as:
Check out the URL: http://some.where.foo/somefile.html.
the period on the end is just a sentence period, and not part of the URL.
Some client software cannot support newer GIF file formats. Saving the GIF in a "87A compatable" format in (Gif Converter will do this) fixed the problem.