This can happen from several reasons, but the key concept is to remember that IE and FF read the parameters differently and that FF read the tag and IE uses the tag.

Now try the following:
1. Note that the parameters should not have any whitespace in it. FF will work with it but IE will not.
2. the allowFullScreen must be set to true (see if this is being done in the generated html when using JS helpers)
3. Using swfObject - try to set the minimum version to 9.0.115,0

If it worked for you or you had another experiance - tell me.
Thanks;
David