r.mfilter

[Dan Riker]

Hello there, I hope all is well.
I have a question about r.mfilter.  I have tried using it on both 4.0 and 
4.1beta, and i have gotten "ERROR: matrix: can't open filter file"
I have tried using 'n' also as the filter, and the other filter types.
Has anyone experienced this in either version?  It seems that Grass works
well in any other situation, so I don't understand it.
Any hints?
Dan Riker
Duke