Is It Me or the Camera?

Try restarting Windows and/or changing the usb cable you are using to connect the camera; that helped me in the past when I had similar non deterministic errors.

If the USB cable is not the issue, uninstall the ZWO driver and reinstall it.

My ZWO ASI 2600MM camera also occasionally fails during a download and shows the same message, also when using NINA. It can also happen during a plate solve, autofocus, or calibration frame. But it only happens very occasionally and doesn’t represent a real problem for me. If your camera has decided to only do autofocus exposures, then the issue is indeed serious. It seems that the USB cable is functioning for autofocus, although it’s always a good idea to try a different one. ZWO’s software usually causes few problems and tends to be up to date, although it’s also worth trying to reinstall it. I wouldn’t touch the camera’s firmware without consulting ZWO first. Lower the USB limit in the camera tab of NINA if it’s set above 40. Make sure your power supply is delivering 12V (I’ve had issues with faulty power supplies or cables that were too thin and only provided 11 or 11.5V). I find it interesting that the frames that do work are done using the Hocus Focus plugin. Maybe the issue lies in the NINA or Hocus Focus update. Have you tried disabling it and using the regular autofocus instead?

Here's a different issue that occurs while using PhD2. I've had the same message pop up a few times. 

Occasionally, especially if you made some changes to your rig, PhD2 will connect to your main camera, 2600 or 533 for instance, instead of your guide camera. So if you have PhD2 open for polar alignment, it will interfere with NINA. 

This just happened to me Sunday night and it took me several minutes to realize what was going on. Of course it didn't hit me until I started and restarted both NINA and my miniPC.

Check your power supply for your camera. I had weird issues when. I wasn't getting enough power to the 533.

+1 for the cable. I got that error using zwo's orange USB3 that came with the camera. I thought maybe it was traffic due to simultaneous download and SSD writes, but it would occur at random times. I spent $50 on a higher quality cable from a reputable supply company and haven't had the error since. YMMV
Tom

I may be wrong, but there may be a problem in the following.

I've encountered a similar problem. I use the ZWO ASI533MM as the main camera, and the ZWO AI120MM mini as the guide camera. When working with NINA and PHD2, the main camera can connect to PHD2, and then the error ZWO camera driver error appears in NINA.

There are no problems when working with Asiair with any cable.

Were you using the ZWO supplied cable? I have experienced usb cable failures right out of the box. I've replaced most of mine with new, higher quality cables.

Jose - Yes, the binning was set to bin 1x1. Like you, I don’t understand why they downloaded correctly.

Scott - Yes, the cable failed right out of the box. It’s a USB 3 and two metres long. I had a two foot USB 2 that I replaced it with and it appears to be working just fine.

I recently bought the qhy minicam combo, the supplied usb 3 cable feels like it was designed to charge a Tesla. The difference in cable quality between qhy and zwo is stunning if that example is anything to go by.

I've had good luck with the ZWO cables but unless you pull one apart and look closely at construction and check operation with a cable tester, any one experience is purely anecdotal. I have data to back it up but I'm my feeling is that cables are often blamed when other details are the cause, like poor connecters on the mount or camera. USB is not even close to an industrial grade, reliable connection but that's what we have to deal with.

Cameras

andrea tasselli:
ZWO's cables still going strong after 5 years...

I had one of their red usb 3 cables dead on a brand new camera. I thought it was a camera problem, very thankful it was a cable. lol