Confidence Interval: getting "NA" as an answer. Why?

of course. The summary looks as follows:

> summary(data)
   Individual         Age            gender          Distance      Challenge         help       
 Min.   : 1.00   Min.   :20.00   Min.   :0.0000   Min.   : 529   Min.   :1.00   Min.   :0.0000  
 1st Qu.:23.75   1st Qu.:21.00   1st Qu.:0.0000   1st Qu.:1107   1st Qu.:1.00   1st Qu.:0.0000  
 Median :46.50   Median :22.00   Median :0.0000   Median :1367   Median :1.00   Median :1.0000  
 Mean   :46.50   Mean   :22.61   Mean   :0.4674   Mean   :2345   Mean   :1.63   Mean   :0.5652  
 3rd Qu.:69.25   3rd Qu.:24.00   3rd Qu.:1.0000   3rd Qu.:2079   3rd Qu.:2.00   3rd Qu.:1.0000  
 Max.   :92.00   Max.   :29.00   Max.   :1.0000   Max.   :8890   Max.   :3.00   Max.   :1.0000