plots sent to to a chart tab do not show plot & I loss the plot
 

I have a spreadsheet that has a chart tab with a plot of data from another
part of the spreadsheet. Now, however, the chart is empty and when I try to
send any plot to a chart tab the plot is lost and the chart tab is empty.
This is happening now in all my spreadsheets the plot can be created within a
spreadsheet but as soon as I move it to a tab the plot is lost and the chart
tab has nothing in it. !!!????!!!!