could not start print job

Thanks all for sharing your experience. I had the same "could not start print job" on my P900 and Lightroom Classic.

I followed the "Greyscale" suggestion and in Lightroom/Print, Page setup/Properties, changed "Print mode" from Colour to Advanced B&W Photo (a small change from Greyscale).

I then closed down Lightroom, opened it again and reset the Print Mode back to Color.

Printer was then working OK again.

Here's the fix which works/worked for me:

Precondtion: Properly set-up user templates with printer properly set-up in the "Page Setup..." dialog in the lower left corner. I.e. you should be able to simply select the template and the photos and click "Print".

1. Click on the lower right button labeled "Printer...".
2. Simply click "OK" in the popping-up printer dialog. No changes needed. The (new) print job starts.
3. From now on, the "Print" button works again.
4. Don't forget to cancel the hanging print job in the progress bar in the upper left corner of the LR window.

Some background: The error is reliably reproducible only for my plain paper template (Color management: Managed by Printer; Standard settings in the printer driver). Win 10. Epson driver. 

NEW: I have just poked around a bit: After I have changed a printer setting (high → standard quality) via the "Page Setup..." dialogue, and updated the template with the new settings (right click on template, "Update with Current Settings"), the problem seems to be gone for my mentioned plain paper setting. Switching back to the old settings didn't invoke the problem again. So looks like the template file was corrupted. 

I started getting this message in febuary, talked with tech support the said it was a corrupt catalog created a new one aftyer 10 prints got the same message again. I can print the same file from photoshop with no issue .  after reading  Jims mention about profiles I deleted the ICC profile I was having an issue with and reinstalled it so far it seems to be working. we will see as time goes on, my machine is windows 10 version 1909. thanks for everyones info.

I don't know if your problem is the same as mine. I'm using Windows 10, and there are more than one instance of my printer driver. If I choose the wrong one and then Lightroom indicates that the printer isn't ready. Then I have to switch to the other one which has a (1), and then Lightroom will print. Other times I have to switch to the other one. Haven't taken the time to figure out which one to delete in my Windows configuration.