Looks like a problem with the cov.names argument, not cov.  Can you make 
a stand-alone example showing the error?

Allan.

On 29/06/09 14:31, Jenkins, Helen wrote:
> The error message when I use list is:
> " s.matrix(!is.na(new.data[, cov.names])) :
>    invalid subscript type 'list'"
> [...]
>    

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