When I try to open a large TIFF image I get the following error "Unable to load test.tif" as a picture. This happens for all large TIFF files.
Here is an example. I had to upload it because it is 400mb.
Is there any particular reason that this image has a resolution of 2400 dpi? If you reduce its resolution to 600dpi, the file size, of course, shrinks dramatically and it will display fine.
Depending on what you do with your pictures - for instance print on an ink-jet printer - 300 dpi should be good enough.
You are just wasting disk space and increasing image editing time by working at such a large resolution, unless you have a very good reason like printing billboards.
DPI has nothing to do with image dimensions (pixels) neither file size. It has only meaning when you produce a physical image from a file.
I have films/slides scanned at 2700 or 4000 DPI. They are exactly the same size/dimensions on disk if I change their metadata to 300 DPI.
This image is probably just too big for DO viewer.
I don't want to be disrespectful and I appreciate your help, but reducing the image quality to be able to view a picture in an image viewer sounds like an absolutely ridiculous idea. 
At that point it might be better to switch to a different image viewer. Windows "Photos" has no problem viewing the image. Also the DPI and resolution works fine for a PNG image. So there are plenty of workarounds. But nedless to say, I would like to continue using dopus. The reason why I posted this was to find out if this is a limit/bug or intended behavior.
I completely disagree with you and I do have a very good reason to use high DPI. Also I do not have a disk size problem. I could of course write a long post about why people are stupid for not using high DPI, but I will leave that discussion for another time 
I am glad you have plenty if disk space. Photoshop says your tiff image is 1.56 gigs in size. It takes around 12 seconds to open. Duplicate the layer a couple of times and the file size is simply enormous. Extensive Photosshop processing becomes a truly laboured business.
I spent 25 years working in the electronic imaging business. Even for the glossiest of magazines we would use a Crosfield drum scanner at 1200 dpi to produce scans. For a web offset newspaper press, 200 dpi was more than adequate.
It is the file size that ultimately matters not the dpi. If you convert your image to a 600 dpi tiff to the same 1.56 gig dimensions you will see that it will display in the Opus viewer very nicely - if somewhat slowly
If you added image metadata and keywords to a couple of hundred files a day opening each in the Opus image viewer you would soon get fed up of 1,56 gig files I can tell you, but then apparently I am stupid. 
We'll have a fix for this in the next update.
An 24bpp image with those dimensions is near the limits of what most of the Windows bitmap APIs can handle, and a 32bpp image is beyond the limits.
We can make some changes to make things work in more cases, including this one, but there are some hard limits if you go much larger or need an alpha channel (32bpp).