No, because it is not a straight sum. It is a mixture of addition and subtraction within the range. When it was totally addition, Excel ignored the text, but once I introduced the subtraction, it returned an error. Thanks, but I think Colin has solved the issue.
Oh, man, so simple! Of course, splitting out the formula into 2 straight "sums" functions allows Excel to ignore the text. I thinnk this is a case of not being able to see the forest through the trees. Many thanks, Colin.