You may have already done this.
Delete the plugin and redownload and reinstall.
Greg
EDIT: I read your post a little more carefully.

The centre wheel defaults to incremental. This was changed to be this way after a few of us users requested it.
If you want to use centre wheel as continuous the you need to assign one of the buttons to select continuous/incremental.
My self I can't see the need as the outer wheel already does this.