hi Frogsy, i have the same exact problem...but i can't get past that warning.
Whether i click OK or CANCEL i get the same result: that error message telling me my .ost file is not valid & then it shuts down.

Did you find a solution to this?
I even tried a "fix it for me" thing on the Microsoft site to uninstall Office fully but it didn't work.

thx for any info or help!!