Peter N wrote...
I am using Excel 2002. It seems to be unable to handle any more than
16
predictor variables. All it returns is a #REF error. The help does
not
document any limit. Is this an undocumented limitation? Is Excel
2003
LINEST capable of handling more that 16 variables? How many?

What's your *EXACT* formula? LINEST should return #VALUE! and #NUM!
errors when it can't invert the bilinear form of the independent
variables, but it only returns #REF! when there's a true range
reference error.