Did you upgrade using Waninkokos or another Updater other than the original way?
If you have homebrew channel install, just look for DVDx boot.dol file, then run it using the HombrewChannel.
I already had it install before I updated, but should install if you updated without all the patches.
Theres a possibility that it might not work tho depending on what you did.
What about if one wants to use USB2.0 and needs the 'advanced' option to select ISO202?
This is from the mplayerce 0.5 README.txt
You need to install the USB 2.0 cIOS from http://wiibrew.org/wiki/CIOS_usb2
You must then then reinstall DVDX http://wiibrew.org/wiki/DVDx using advanced
mode and selecting IOS202. Even if you don't plan on playing DVDs this is
necessary for MPlayer CE to detect if the cIOS is installed.
Users with system menu 3.4 or higher will not be able to use USB2.0 with
MPlayerCE because the DVDx installer for 3.4 does not have an advanced mode.
Unfortunately there is nothing we can do about it.