My charts became uneditable

[acb764se]

Hi all.

I have a Xcel-2010 workbook with 3 sheets, the 1st is unused, the second contains a table of gas and electricity usage in my own home (columns) as a function of dates (rows) and the 3rd worksheet contains 2 charts with data from the 2nd worksheet.

These charts are still alive, when I insert new data new points appear. But they can't be selected or edited: the top chart covers most of the bottom one, I used to select the bottom one and bring it up front in order to view it, now it's not possible!

When I move the cursor on both charts it still says "Chart Area" and "Plot area" in the right places, and "Data blah-blah" when on the data points, but the right mouse button does nothing at all.

How could such a thing happen, and (more important!) how can I fix this?

I googled and found suggestions to click Options-Advanced-Show All in this worksheet, and also saving as a previous version, but the problem is still there.

Thank you for any suggestion!

PS Immediately after posting I thought of copying the problematic worksheet, and see if the problem persisted. But Xcel told me "Command unavailable in a shared workbook" Astonished! Shared? By whom? With whom?
So I googled for that, and found a suggestion to go to the "Review" tab, click "Share workbook" and uncheck "Allow changes by more than one user at the same time". This worked, and my charts are again functional.
Thanks all the same for reading about my problem!