Just fixed my no sample error. Mine was clogged at the junction fitting for all the tubes. After flushing and trying all the priming and reset settings within the software with no luck, I shined a flashlight into the back after removing the tray and saw some discoloration in between the solenoid and the center junction box on the clear line around the 10/11 o'clock position. The only way to clean this is to disconnect the unit, remove the 4 rubber feet screws at the bottom and remove the cover. I the used my fragging tweezers to remove all the tubes from the junction box (remember how it came out, you may want to mark the box). I then had to clean the blockage with a pin and then flushed with a syringe to ensure all the crud was out. When reassembling, I noticed that the tube and fittings were slightly different sizes which is why you should mark. The 3 smaller fittings on mine went to the top and the larger at the bottom. If you get it wrong you'll notice loose lines or struggle getting them on.
Plugged it back up, it initialized, then I ran a combined test, back to normal. In my case, it was good that I fixed it within a couple days because the last test were extremely low causing it to max out dosing trying to catch up. Guess it's a good thing you can set the max which I think is 5% +/- on mine. My alk was 6 on the last test it took. Last good test was 8.12 and first unclogged test was 8.21 so I'm breathing a sigh of relief.