If the player appears to hang with a black screen on startup (but pressing Display still works), and it is a network-aware title then you may have hit a problem with the downloaded content.
If this is all true but you still cannot connect to the networked content, check the support site for the disc you are using (many of the network error dialogs will include an error code and a web address to check for more assistance).
The Xbox player is pretty good at recovering from read errors once the movie starts, but read errors in critical areas of the disc used to start it up will cause this error.
If the movie starts up then dies with an error blade, note the error code (which is an 8-digit hex number). Error codes are caused by either bugs in the content on the disc, or by bugs in the player software itself.
If you are lucky you will see an actual movie name, and you can select it and delete its pstorage.
However many titles right now will show up as "Unknown Title", so to delete one you will need to guess which is the one you want to delete.