Welcome to
MY world ...
TC, may I just say, for now, and until we hear from Captain Boinc, Ady, is ...
ignore it.
Do not reset, eventually it will finish & will be OK and you'll get credit.
I am beating myself around the head trying to "fix" this same "error" on the Old Girl ... as far as I can ascertain, with my PC that is, it has something to do with the bad way PCs keep time ... I stress ... I seemed to be alone in all things that can go wrong in Boinc, do go wrong on my PCs.
From what I have read, this can happen to "normal" PCs and clears itself. So, hang in there and ave a cuppa.