The formula or graphical indicator may contain an error but cannot be sufficiently validated because an instance of Microsoft ...

The formula or graphical indicator may contain an error but cannot be sufficiently validated because an instance of Microsoft Project Professional 2010 is currently running on the computer. To correctly validate the formula or graphical indicator, 
Project Professional must be restarted.

Do you want to automatically reload Microsoft Project? Warning: You may be prompted to save currently loaded work."