And we can't help you without a much more detailed description of your database and this specific layout.
I think i have found a bug
when i placed a chart on to a layout i could amend the chart data but could not add any data to a record even if is added a new record this happen 3 times and when i inserted the chart at the start of a new tab control and no fields it worked which i would not have expected i was expecting no access to the record then i found the if i had fields in a table if i deleted those tables and reinserted them the problem then cleared it self
Like Phil said, more detail please. Without the details I assume it's your error and not a bug.
More detail as in what version of Filemaker are you using? In what layout part did you place the chart? What kind of chart--in particular what data source options did you select?
A screen shot taken of your layout while it is in layout mode would also be helpful.