Thanks very much for your continued interest G@M3. I have just found out from an article by Keith Sketchley (http://ourworld.compuserve.com/homepages/sketchley_keith_h/cdinfo.htm) saying that DirectCD has exactly the same problem (Keith’s article also has a number of other very good points of general interest re CDs).
He mentions that one answer is to reset Windows, and I’ve found that this does work, but is clearly only a workaround rather than a solution. So it seems two of the most popular CD-RW packet writing writing programs effectively have a bug that causes this read-only problem. Perhaps it will be cured in future upgrades. However, as mentioned, Ahead Software (InCD) rarely respond to technical queries from users.