universal kriging

[Marlous van der Meer <m.vandermeer@geog.uu.nl>]

Hello,

I have a slight problem with universal kriging. I have a data set
consisting of several files of measurements of a beach profile
(x,y,height/depth). The measurements are from the shore (about 1 m.
above sealevel) to the sea (varying, but about 8 m. below sea level) and
consist of several transects parallel to each other. I want to know how
this beach profile evolves through time. 
To interpolate between these transects, I use universal kriging. I have
created a map with the distance of each cell to the coast and added
these values to the ascii data files. Then I made the command file to
execute universal kriging. 

Command file:
point(profiel): 'afst0707.txt', x=1,y=2,v=3,X=4, radius=125, min=1,
average;
variogram(profiel):0.13 Nug(0)+ 4.59 Gau(254);
mask:'afstand.map';
predictions(profiel):'tmp.prd';
variances(profiel):'tmp.var';
set zero=0.001;

But my command file keeps crashing. 
Gstat gives me the following error:
gstat caught an error that occured in the atrix library, the reason for
it was: singular matrix.

As a sollution it gives the option to add 'average' to the data
definition (I had already added it before running the command file) or
else to set the variable 'zero' to a larger value. This last option I
executed, but this also didn't help. I tried several values for the
variable 'zero'. 
The funny this is that not all the command files crash for this reason,
while all the ascii files have the same build up. 

I don't know how to solve this problem. Can anybody help me?

Many thanks,
Marlous van der Meer