it might be because youve applied a IK spline to control the spine and therefore the joints are linked via the IK spline, thus not allowing you to rotate the joints (as they are controled by the IK handle)

What I think you mighe be needing is a FK spine, or a FK/IK swither, if you look on google theres lots of tutorial for creating FK/IK blends ( you basically change a setting in the IK handle tool that allows you to go between FK/IK, the most common example is in the arms of a character.)

Hope it helps, if you've not aplied a IK handle to the spine then i'm a but stumped, unless youve locked out the rotations??