SpatStat Kest - Error Message help

Hi I'm working with the function Kest in the package SpatStat (under LINUX
with R 2.1.0). In order to evaluate the statistical significance of my
point pattern I'm doing 999 Montecarlo replications. The script that use
the Kest function runs OK for most of the different point patterns that I
have but for a particular point pattern, which have only 17 points, it
runs until the 34th iteration and then I receive this message:

Error in "[<-"(`*tmp*`, index, value = NULL) :
	incompatible types (1000) in subassignment type fix
Execution halted

Do you have any idea about what could be the cause of this ? Thanks in
advance.

This is not an error message from 'spatstat' itself.

  The message has been generated by the function "[<-" 
  which is called when you assign values to a subset of a dataset 
  (in a command like x[z] <- v). The message appears to say that the
  replacement value v is not of the same type as the original vector x. 
  
  You say that you are running a "script that uses the Kest function".
  The error is probably inside that script. If you send the script to us
  we can probably spot the problem for you.

  As Rolf mentioned in his email, spatstat provides a command "envelope"
  to compute simulation envelopes. This might be sufficient for your needs.

regards
Adrian Baddeley