TIFFs does not show in Preview app or DVDSP

I'm rendering TIFFs for subtitles using Belle Nuit.

The TIFFs (either TIFF-RLE for Final Cut Pro or TIFF-DVD for DVDSP) are generated just fine.

But they do not show when using the default Preview. Preview Inspector just says "No document"...(!)

I can view them just fine in Photoshop, QuickTime player 7 or other apps.

And the TIFF-RLEs works just fine in Final Cut Pro (but I can't look at the TIFFs beforehand using Preview).

Now, the problem really is that DVDSP does not show the TIFFs/subtitles at all - and that's a problem. The STL Graphics file works just fine. The TIFFs are placed on the Track just fine, but they do not show at all.

What might have happened? Checking one of the TIFFs, I have read/write access to the file.