levelplot gives an error

hello

why does levelplot function give an error

OK_pred <- krige(z~1,el4, newdata=mask_SG, model=efitted)
levelplot(var1.pred ~ x + y , OK_pred , aspect = mapasp(OK_pred), main = 
"ordinary kriging predictions")
Error in eval(expr, envir, enclos) : invalid 'envir' argument

regards

-- 
Ahmet Temiz

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