I ran across this trying to use the named formula CostBudgetWeek (named formulas are also sometimes called named dynamic ranges). Names that begin with R or C don't work in SERIES formulas. Oddly, they are perfectly valid in worksheet formulas.

This problem was very difficult to troubleshoot. Thanks to the folks over at SuperUser who solved this in 2012.

My problem was easily solved by renaming to xCostBudgetWeek.

The thing that makes this very maddening in that if you enter an illegal name in a SERIES formula and hit ENTER, nothing happens. Nothing at all. There is no error message as when you enter an illegal formula in a worksheet cell. I am surprised that this non-response to an error persists.

I use Excel 2013. Apparently this problem also existed in 2010 although I don't know how far back it goes. Haven't tried it in 2016 yet. There is some thinking that this is an Excel bug, somehow related to rules for names intended to prevent collisions with ranges that use the R1C1 naming convention.