Error creating chart in report

Hello,

I'm trying to add a chart in a report already in use by my company.
I receive every time the same error message :
"Check to make sure that the column(s) selected for the chart series are numerical values. Error: x-axis offset is out of range: 39599.0."
I do a lot of tests changing format and values of the series but I receive always the same error.
I'm using CF 8 with a MS SQL 2000 server on a Windows 2003 server system.

Could some one sugest me how to avoid this error ?

Thanks,
Davide