If you have ToB installed then stalkers cannot dual. For your avenger you need 17 strength which you cannot have which is why you cannot dual from an avenger.
To dual you need 15 in your current class' prime requisite and 17 in the class you want to dual to.
Hmm, perhaps you don't have to uninstall ToB : just open and edit dualclass.2da in teh Override folder, it's a simple text file that lists possible duals. I don't have it right now (I'm at work ! ) so can't give you detailed procedure but it's somewhat straightforward.
For your Avenger edit it and give him 17 STR with Shadowkeeper !
So you can still enjoy ToB !
I tried editing this file once but all I managed to achieve was to get the dual class button there. To actually dual from say a ranger to a mage was never possible. Am I doing something wrong?
So by changing this .2da file you could possibly dual class a paladin or perhaps dual into a kit. Or edit it so that rangers can dual to any class? Do you think you could give more instructions on what you have to change.
) so can't give you detailed procedure but it's somewhat straightforward.