R help - Jul 2011 - LogLik warning() corresponding probabilities for node ... were 0 or NaN.

Hello R Helpers,

I am trying to find the log liklihood between the bn.fit of one set of  
data and another.

At small sample sizes I get the warning  message

In FUN(c("...", "...", "...", "...", 
... :
   1 observations were dropped because the corresponding probabilities  
for node ... were 0 or NaN.

Is this due to the size of the datasets, I have tryed it on larger  
Datasets and it works, or am I doing something wrong? Is there anyway  
around this?

Many Thanks

Liam