ReviseQuoteRequest doesn't work for active in progress (R/O) quotes

What message (or other process) can be used to revise a quote which was activated in UI (by clicking Activate Quote) and has a state/status of In Progress/Active? I have tried using ReviseQuoteRequest which, based on what I've read, should work but when I run this code I receive an error which states the quote "can't be revised because it's not closed":

                        ReviseQuoteRequest req = new ReviseQuoteRequest();
                        req.ColumnSet = new ColumnSet(true);
                        req.QuoteId = new Guid("B0E98FCF-4BD0-E511-B5F1-00155DFA52CB");
                        ReviseQuoteResponse resp = (ReviseQuoteResponse)proxy.Execute(req);

I am attempting to replicate (in C#) the same functionality behind the click of the "Revise" button on the quote ribbon (set the state to Draft and increment the revision number).

Thanks.