nlme package dependencies?

Dear R-help,
The following nlme example, from help(Variogram.gls), does not work on my
system.

data(BodyWeight)
fm1 <- gls(weight ~ Time * Diet, BodyWeight)
Variogram(fm1, form = ~ Time | Rat)[1:10,]

Error in FUN(X[[1]], ...) : unused argument(s) (method ...)

It looks like I might not have loaded a necessary package.  I did load nls
and lattice (the latter not actually being listed in the package description
as a dependency).  I checked the R-help archives thoroughly and also
examined the library nlme scripts.  The chapter 5 Wheat2 example from
Pinheiro & Bates (2000) didn't work either:

library( nlme )
library( lattice )
data( Wheat2 )
fm1Wheat2 <- gls( yield ~ variety - 1, Wheat2 )
Variogram( fm1Wheat2, form = ~ latitude + longitude )

Error in as.data.frame.default(x[[i]], optional = TRUE) : 
        can't coerce array into a data.frame

Apologies; here is my system information:

R.version

_              
platform i386-pc-mingw32
arch     x86            
os       Win32          
system   x86, Win32     
status                  
major    1              
minor    4.1            
year     2002           
month    01             
day      30             
language R              

Thanks.  R is great.

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