Complex sampling in SPSS - Deff var is blank

Using spss 15; have plan set up and used it with the analysis.  Calculating effective sample size for a methodology report.  

Used this command:

* Complex Samples Descriptives.

CSDESCRIPTIVES

 /PLAN FILE = Path+'\C2010only.csaplan' 

 /SUMMARY VARIABLES =quality 

 /MEAN

 /STATISTICS SE DEFF.

OUTPUT IS: 

Univariate Statistics

                 Estimate Standard Error Design Effect

Mean quality     1.69   .030                   .

PROBLEM:

The deff is missing.

Any idea as to why?

Thanks,

JL