Hi Darren.
There's quite a bit information here regarding that error number.
http://www.updatexp.com/c00d11ba.htmlHave a try with the suggestions posted, but before you do that try something simpler. Usually, and I've experienced this myself, if Windows Media Player systematically goes through an entire album, and shows a red x for every song, then it's possibly because it can't find them anymore.
Either they've been moved, the album name changed etc.
You can try this by opening an album and then right click on one of the tracks that won't play, and select "Open File Location".
If it finds it OK, then it's something else causing the problem. You could make sure it's not a file association problem by opening "Tools\Options\File Types" and click the "Select All" button. If you have other players as default, you can reset the default file association later.
If that still makes no difference, then have a look to the suggestions at the above link.
Hope that helps.