Used to happen to mine, and I lived with it for a wile, when you get the error click Continue, then go back to the Start tab, then click Items again - the tab will now be working, but will have broken the search button.
I believe the error happens because this version of Fiddler is trying to load 65,535 items, when it should be reading 49,151 entries, starting at ID offset 16384 to skip land blocks.
I did manage to fix my by accident, simply by clicking "reload paths" in the options. I also manually typed out the path in the very top box and applied that to all of the files. After that, it has been running like a dream with full UOP support.