Why i have a red question mark Constraint in Creo CETOL Lite?

Hello,
Why i have a small red question mark above Constraint in measure difinition's name column of Creo CETOL Lite like this?

This problem makes me can't get the correct analysis data. Would you mind telling me what's wrong?
You also can see the problem picture in this link: http://i2.bvimg.com/1949/83b1abb7f5f03d76.png