Hello,
I was having the same issue and went through all the steps and checked everything. Then, I reread the article, and it said something about displaying circular references in the toolbar in the bottom left corner. I looked and it displayed "Circular Reference E134." I went to the cell and sure enough it was there! I deleted the formula and then went through each tab (I had copied this sheet for months) and found the circular references and deleted them. It was made most likely when I was clicking and dragging things. I got so used to just clicking "Okay" that I stopped worrying about it...sometimes....hope this helps.