I have found myself the problem. 
GRASS has a problem when using i.tape.other with files with
names longer than 20 characters.
Normally when you mount a SPOT CD-ROM you save the image file
in some directory. While running i.tape.other you are requested
Enter tape device name:
and this is normally longer than 20 characters.
So modify the main.c and change the variable "name" to a value
greater than 20 (i.e. 100) and recompile it.
A final word about SPOT.
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After reading the file check carefully the histograms you will
get and compare with that ones supplied by your vendor.
Regards
Juan.Jimenez@cedex.es