Yes, the “marker errors detected” message that PrintDraft gives appears to be somewhat unconnected with the markers checking tool. I think the word “marker” in the PrintDraft warning is probably a mistake, and that you’re actually failing one of the other basic checks.
In practice I ignore that PrintDraft message. If the pdf compiles successfully, I’m happy. If it doesn’t, I start running through the basic checks trying to fix the problem.
Note that sometimes the PrintDraft appears to complete, but if you check carefully you’ll find that the Scripture range is truncated somewhere in the middle. Don’t assume everything is perfect just because you ended up with a pdf.
Remember that you can hold Control while clicking the OK button in the PrintDraft menu. This will allow you to look in the PrintDraft folder and read the .log file to discover what is going wrong.