I've been working on a new WB skin for a while. Created and edited primarily in SKS6, although I've had it open a couple of times in SKS5 to set System Fonts, etc.
Anyway, I went to open it in SKS5 again a day or so ago and got this weird error about the skin being a UIS1 skin and not being supported by SKS5. Here's a screenshot of the error

I believe this is the first time trying to open the skin in SKS5 after working on it with SKS6 ver 6.00.003, which I recently upgraded to with SDC. I haven't tried editing any other skin in the latest SKS6 yet to see if I get the same error when opening the skin in SKS5 afterward.
Anyone seen this or have a clue what caused this ... other than the possibility of the newer SKS6 changing something in the skin that SKS5 didn't like?