I'll say it again, what you are doing has absolutely nothing to do with Qimage or Overdrive so I want to be clear: Qimage and Overdrive are always working!  There is never an instance where "overdrive doesn't work".  Overdrive is working fine.

What you are running into is what I've been telling you from day one: no inkjet printer can actually produce 1200 PPI on paper.  So what you are running into is the fact that 900 PPI gives you just enough detail to be able to discern individual frames (lines in this case).  Going beyond that, the hardware simply cannot handle it.

Also, the demo didn't operate any differently than the registered version and... it didn't work sometimes and not others: it worked every time.  What is happening is that depending on what you print, how sharp it is, and how much it differs from frame to frame, some images (or areas of images) may look like they have some separation at 24 frames while others will not.  And we are back to the bottom line which is, you are asking your printer to print beyond its hardware capabilities.  Overdrive will help (as you found out) but it is not a substitute for hardware limitations.

It's sort of like going to a Chevy dealer and taking a Corvette for a test drive.  Later you express concern with the dealer after you buy it that it won't go 210 MPH like it did on your test drive.  Then the dealer finds out you measured your speed on the test drive on a 10 percent downhill grade with a 40 MPH tailwind.  The car is doing the same thing every time.  You just can't expect it to reliably perform beyond its specs 100% of the time.

Mike