Hi Sharker
It turns out it has nothing to do with the above at all.
We spent about 3 hours yesterday going through everything and by chance happened upon a solution but can only make guesses as to the actual problem.
I work for a company whose intranet is based heavily on MOSS. So we are trying to build a few small apps to get started with silverlight.
The problem appears to be a quirk of MOSS (or perhaps more specifically it only happens in certain templates used in MOSS and maybe an issue with the templates). If you add a silverlight movie to a page it doesnt appear until mouseover. Once we started to get a handle on things we could consistently reproduce the problem regardless of the browser.
Next we noticed if we had 2 movies on a page, the first would appear as normal. Or if we had a javascript based widget after the silverlight the movie would appear.
Eventually even loading something very small such as a very small external css file in a module after the movie, triggers the movie to load as normal.
So our solution is to have the last module to load on the page to load a very small css. The module has the title bar switched off and is invisible to the users. Doing this loads all movies on all browsers. It appears to work consistently for all users.
Now, why this works is guess work. Whether its loading something external causes a small update to the DOM which is enough to trigger the movie to display, I don't know but it appears to work
Regards
John