[Gfoss] v.vol.rst

[Luca Cinquepalmi]

Hi all,
I have an ascii file with 4 fields: x y z w. I want to interpolate these 
points in order to obtain a 3d map. To do this I first create a vector 
map using v.in.ascii command, then I use v.vol.rst to create the 3d map, 
but when I run the command this error appears:

ERROR: Unable to get layer info for vector map

What doest it mean? can anybody help me suggessting me other possible 
solutions? Thank you very much

Luca