Could be almost anything I guess. Mod_rewrite is a can of worms! Evil worms.

So the condition isn't being triggered? Have you tried getting rid of the ^ anchor in the QUERY_STRING line? Just before t=([0-9]+). Not sure if that will help, but I don't know if an anchor should be there, so it may be worth a try.

EDIT: That said, it worked on my test server. So I technically have no idea.