Review and Correct Errors

Select a cell that contains a green  triangle in the upper left corner.

Click the Error Smart Tag button.  Click one of the troubleshooting options:

To have Excel fix the error, click one of the available options specific to the error.

To find out more about an error, click Help on this Error.

To remove the error alert, click Ignore Error.

To fix the error manually, click Edit in Formula Bar.