Degrees of freedom

Hello,

I have a little problem about degree of freedom in R.
if you can help me, I will be happy.
I used nlme?function to analyze my data and run the linear mixed 
effects model in R.
I did the linear mixed effect analysis in SAS?and SPSS as well.
However, R gave?the different degrees of freedom than SAS?and SPSS did.
Can you help me to learn what the reason is to obtain different 
degrees of freedom from R?

Thanks 

Umit?Tokac
Graduate Student 
Measurement and Statistics 
Florida State University
Tel:????????????(850)345-7487??????????????????