Hi,
thanks for getting the screenshots working

Fortunately it makes it fairly easy to tell what the problem is.
You are using the 'Telescope Simulator' mount, and that will not accept SharpCap sending a new set of RA/Dec co-ordinates to it via the 'Sync' command because it is not in tracking mode. This makes sense, because it is trying to simulate a real GOTO equatorial mount, which only has a consistent set of RA/Dec co-ordinates when it is tracking at sidereal speed.
The fix is simple - before trying to do the plate solving, press the 'Tracking' button in SharpCap - that will put the mount into sidereal tracking mode (the picture to the right of the tracking button will change from a '?' to a star to indicate the tracking is at the sidereal rate). Once this is done, you should be able to use the plate solving without any error.
Hope this helps,
Robin