Here's (roughly) what I did...
I deleted my vsdelta directory, opened the file, made one small edit (I think I added a space to the comment) and then saved the file. This gave me the first backup. I then changed these lines:
* incremental processing.
*/
class Taskm : public Model
{
by adding two extra comment lines to this:
* incremental processing.
*
*
*/
class Taskm : public Model
{