I would like to convert the data as is down to money formatting, but it is giving error.
Faturamento.ValorNF = decimal.Parse(RsFaturamento.Fields["ValorTotal"].Value.ToString("#.##"));
Error Message: "no overload for method “ToString” takes 1 arguments"
I wonder what's wrong with my code?
Whatever the type of object Value is, the class definition for it doesn't have an overload of ToString() that takes an argument. If Value is of type object in the collection, you'll need to cast/convert it to a string that is then supplied to the decimal's parse method. Note that the ToString("#.##") doesn't really matter if you're assigning a decimal object to ValorNF as you can always format it at a later time for display.
That being said, if you wanted to format a decimal to 2 decimal places, I'd suggest you use a standard format string for doing so. Below will parse the value into a decimal and then use the ToString to convert it to a string to 2 decimal places:
decimal.Parse(RsFaturamento.Fields["ValorTotal"].Value.ToString()).ToString("N2", CultureInfo.InvariantCulture);