This may be due to an old file, possibly from a previous installation, or one created for another version of Windows. To overcome the problem simply delete the offending FilterTree.xml file and let PMB create a fresh one.
To do this:
(1) If open, close your PMB.
(2) Using your Windows Explorer go to the "Sony PMB" folder (usually a subfolder of "My Documents") and locate the offending FilterTree.xml file.
(3) Delete it (or, if you are nervous about doing that, move it to your desktop temporarily).
(4) Using the Start Button (or Windows keyboard key) go to "All Programs" / "PMB" where you should see PMB Help, PMB Launcher and just PMB.
(5) Click on PMB and it should open correctly without the error message.
If you wish to double check, go back to the folder mentioned in Step 2 and you will see the newly-created file (so, if you were nervous, you can now safely delete the old one from your desktop).
