How to solve Gimbal lock in XSI 5.11

Gimbal lock happen when X and Z axis being in the same order after rotating the Y axis 90/-90 degrees. And this will give you no control over those axis. (this happen with rotating in add mode.)
I suggest you read http://www.anticz.com/eularqua.htm !st.

This is my different way to solve that problem :

1. Select your curve
2. Goto menu curves | choose make rotation continues

if still had problem??? try to delete your key ()in your curve then make some copies from the previous key and then make your pose there.

Keep try ;)

wish u luck