Pie Chart - Won't let me select all the needed cells

Greetings!

I have run into a new problem. I have pie charts that I use to represent the percentages per month of each species of birds I have present on my project site. Not all species are present for every month so I just go down the list and select each cell that has a number in it (corresponds to the population). This use to work fine. My pie charts were great and would update automatically as the month progresses. But recently, excel will no longer let me select all the cells I need. It will stop after about 8 cells. That can vary per month I am working on. Is there a particular reason Excel would just stop letting me add all the data I need?

Thanks for the help!
Rhoni

Hi Rhoni
it might help if you upload the sheet so we can look at it. It doesn't seem like there will be any confidential or private info in it, but you might want to check before you upload.

If you cannot select cell is ribbon greyed?

if not - I agree with post #2