I'm getting the same thing. Are we seriously the only two people experiencing this???
I've updated to the latest DCS (Version 2.5.2.20143) and I was prompted to install the Yak-52 after purchasing it, and when attempting to do so was prompted by that message (Version 2.5.2.20143 is not available).
I can't believe that this won't actually be compatible with the latest version of DCS - that doesn't make any sense.
Does anybody know what's going on here?