I want to Dual Class my Kensai. However, the Dual Class button (the one above the LEvel up button on the record screen) never seems to be highlighted. The manual didn't mention Kensai as part of those who can't dual class, yet I can't seem to do it. What might be wrong? Also, if I ever figure out how to switch, what level would be good to turn mage? Thanks.

For your Kensai, you'll need at least 15 STR in order to dual class, and also depending on which class you want to dual into, you will need 16+ in the primary attribute. For example, assuming your Kensai has 17 STR, he must have minimum of 16 in INT to dual to a mage, or 16 WIS to dual to a cleric. Sometimes alignment also matters, like you can only dual to druid if your character is true neutral.