I am a big fan of label expressions but since the label expression does not seem to be working for you, why don't you try Label Classes. Change the Method under the Labels tab to "Define classes of features and label each class differently".
Next, click on the SQL Query button to essentially do a Definition Query for [Lin_typ] = "Major".
Set your Label Field to be [Contour] and then setup the text symbology:
I hope this helps.
Cory