Cannot convert tiff image (unknown field with tag 40000)

[cates]

I have a lot of scanned TIFF images to convert to a PNG format. Most convert fine, but some give me this error and will not convert;

identify: it81530036371326.1.tif: unknown field with tag 40000 (0x9c40) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/837.
identify: No space Tag Value. `it81530036371326.1.tif' @ error/tiff.c/TIFFErrors/563.
identify: it81530036371326.1.tif: unknown field with tag 40000 (0x9c40) encountered. `TIFFReadDirectory' @ warning/tiff.c/TIFFWarnings/837.
identify: No space Tag Value. `it81530036371326.1.tif' @ error/tiff.c/TIFFErrors/563.

I have run identify -verbose it81530036371326.1.tif on the image and I did notice one thing that looks odd (this may be a red herring though!);
tiff:rows-per-strip: 2147483647
Other TIFF images seem to show a more reasonable value (like tiff:rows-per-strip: 2335).

I can view this image in most other programs (windows photo viewer, mac preview etc.) but convert will not work with it at all.

Tried 2 versions on the same linux server - both with the same result;
Version: @(#)ImageMagick 5.3.1 04/01/01 Q:16 http://www.imagemagick.org
Version: ImageMagick 6.8.7-0 2013-10-17 Q16 http://www.imagemagick.org

Any ideas on why, or where to look??

[snibgo]

Your "unknown fields" are warnings, not errors. Your "No space Tag Values" (whatever that means) are errors.

If you put the file somewhere like dropbox.com and paste the URL here someone might try it.

[cates]

Thanks snibgo - so I suppose the question has become, what does "No space Tag Values" mean?

Any ideas anyone?