Spent entirely too much time this weekend dealing with Linux multimedia troubles. Eventually, after reinstalling xine and installing totem and mplayer, I decided on a whim to install RealPlayer 10. Not surprisingly, it refused to load. I uninstalled it and despondingly clicked on a Quicktime file. To my amazement, it worked. Since RealPlayer is unable to play QuickTime files, I suspect that its installation did not make the QuickTime file suddenly work (yet another computing unsolved mystery...). This is a problem, since if it "breaks" again, I am SOL.
The uninformative Totem dialog box only occurs if I use Gentoo's portage to build totem with the gstreamer backend. When I compiled it myself (using the xine libraries, which I have found are more stable), it would run intermittently if I selected a multimedia file. Attempts to run it from the command line or without a file for input caused it to hang, making it difficult to debug.