Why can I only use an Expression to label

[MaryCoburn]

I would like to use a filed in my attribute table to label my features, but that option is grayed out in the label properties.  It will only let me write an expression.  Is this just an Arc10 bug or have I accidently done something that is preventing me from labeling features by attribute? ANd if it is a bug, does anyone know how to fix it?  Some of the features in my map (that I hadn't previously written an expression for) will allow me to choose an attribute.  The features that I wrote an expression for, though, will not let me change to label by attribute.

Thanks in advance

[jessemaps]

Once you've defined a label expression in a label class, the label field drop-down list will be grayed out as you've discovered. To go back to labeling just a field, change the label expression back to just a field name (in brackets) such as [name].
Then the drop-down list will be active again.

[RobertBorchert]

Yes, just open the expression and hit the reset button.

It shows it as grayed out because the drop down is not capable of showing the entire expression.

Once you've defined a label expression in a label class, the label field drop-down list will be grayed out as you've discovered. To go back to labeling just a field, change the label expression back to just a field name (in brackets) such as [name].
Then the drop-down list will be active again.