The expression you entered for a grid property is not valid. The expression is cleared from the property setting.
If you are setting the expression in the AfterRowColChange event of the grid, the error itself causes the event to fire again, leading to an recurring loop of error messages.
Press Cancel in the dialog box to disable the expression. You will not be able to set or change the expression.
The expression contains syntax errors.
Make sure your expression is valid and without syntax errors.
Variables in the expression are not scoped properly.
Make sure that any variables you use in the expression are globally scoped, or scoped to the form. If your expression contains a variable that is local to the function that you are setting the expression in, the variable will go out of scope when the function returns. However, the expression will be evaluated in the future when the grid tries to paint, and this will cause an error.