SpatialGridDataFrame

Hi to all,
i'm new of the list, and i have a poor experience unfortunatly in geostatistic.
I'm working with grass and R in a linux debian pc.
I'm using grass 6.4.1 with R 2.13.1.
I have loaded spgrass6, gstat, lattice libraries to create some interpolated map
by kriging method.
I created the map with universal kriging, and now i'm tryng to write this map in
grass with:

writeRAST6(UK_avampaese,"UK_avampaese",zcol="var1.pred")

but i have this error message:

Errore: gridded(dataset) is not TRUE

I cheked the dataset typology, UK_avampaese is a SpatialPointDataFrame,
and writeRAST6 needs SpatialGridDataFrame.

Which is the procedure to convert the a SpatialPointDataFrame to SpatialGridDataFrame?
Is possible to make this changeover?

I also tried:

gridded(UK_avampaese)=T

but i received this message:

suggested tolerance minimum: 4.61319e-08 
Errore in points2grid(points, tolerance, round) : 
  dimension 2 : coordinate intervals are not constant
Inoltre: Warning message:
In points2grid(points, tolerance, round) :
  grid has empty column/rows in dimension 1

I would like to specify that the prediction grid used as newdata,
is a SpatialPointDataFrame coming from grass point vector data,
who have an irregular boundary and 5 km spaced.

Any hits are very appreced,
bast regards

Eugenio 
 		 	   		  
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