grass - i.maxlik cannot read i.class output signature file

I'm trying to perform a supervised classification using i.class. I'm then using i.maxlik, but this is returning the following error:

GRASS 6.4.3svn (India_01):~ > i.maxlik group=test_group@test subgroup=test_group sigfile=test_sigfiles1 class=test_results1
ERROR: Unable to read signature file 

I'm not sure what other information I should provide. Can anyone suggest the possible reasons for this error? I've tried using i.cluster to generate an unsupervised signature file, and i.maxlik reads this perfectly well.