Hi, I have the same problem in that changesets were created ok, 1 to 5 (for example) and a few other changesets were created which I deleted using the GUI (all good so far).
However, when I manually deleted a folder and replaced it with another and then tried to check in the "changes", PlasticSCM came up with the message "The specified changeset 8 cannot be found...".
I duly deleted the plastic.wktree and then tried to check in changes only for it to now say "The method verison 15 is not supported. Minimum supported version 0. Maximum supported version 1."
Any ideas? Or should I consider it lost and start from scratch?