Knossos might, and in fact probably should, consider version 23.0.0-RC8 to be less than 23.0.0, since RC8 is a pre-release test version. My advice is to your engine stability preference in knossos settings to stable and update FSO so you get the final stable build of 23.0.0
Knossos seems to have some hard to pin down problems with not doing updates properly.
One possible thing to check, if you are using the knossos search feature be sure to clear it out before launching the mod. The search applies not just to mod listings but also to engine version listings, so it can cause that no-executables error.