Hi, you may have resolved this issue already, but if not...
There should be one copy of MediaAccessibility.dll in the folder:
C:\Program Files\Common Files\Apple\Apple Application Support
(32-bit systems) or
C:\Program Files (x86)\Common Files\Apple\Apple Application Support
(64-bit systems)
If you can locate the file, right-click on it and select Properties, then on the Details tab it should have File Version - 48.1.0.11. If it has a different version number then it is out of date and is likely to be cause of the problem.
Please search your Programs Files and/or Programs Files (x86) folders for all copies of the file MediaAccessibility.dll - Any other copies of the file in different locations are likely to be out of date, but might be called in error by an executable file in the same folder, thereby causing the error.
Should you find more than one copy of MediaAccessibility.dll could you please let me know in which other locations it was found. This will let us more effectively help others with the same issue by suggesting where they should look. If you have the correct version, in the correct place, then deleting any others should fix your problem. This is similar to the QTMovieWin.dll issue dealt with in the first box of the user tip Troubleshooting issues with iTunes for Windows updates.
If you don't have the correct version of the file then completely removing all components, deleting the named folders, and reinstalling as suggested in the second box of the user tip should work. You could try repairing Apple Application Support alone from the the Programs and Features or Add/Remove Programs control panel first as that would be quicker, but only if it works.
tt2