jittering when interpolating key frames

JointLocalParams InterpAnimJoint;JointLocalParams &BeginAnimJoint = Frame.Joints[j];JointLocalParams &EndAnimJoint = NextFrame.Joints[j];//////// interpolation!!!!!	float InterpValue = FrameTimer.ElapsedTime()/FrameTimer.IntervalLength;	if( InterpValue > 1.f )		InterpAnimJoint = EndAnimJoint;	else if( InterpValue == 0.f )		InterpAnimJoint = BeginAnimJoint;	else if( BeginAnimJoint.Rotation == EndAnimJoint.Rotation )	{		InterpAnimJoint.Rotation = BeginAnimJoint.Rotation;		D3DXVec4Lerp( &InterpAnimJoint.Position, &BeginAnimJoint.Position, &EndAnimJoint.Position, InterpValue );		D3DXVec4Lerp( &InterpAnimJoint.Scale, &BeginAnimJoint.Scale, &EndAnimJoint.Scale, InterpValue );	}	else	{		//D3DXQuaternionNormalize( &BeginAnimJoint.Rotation, &BeginAnimJoint.Rotation );		//D3DXQuaternionNormalize( &EndAnimJoint.Rotation, &EndAnimJoint.Rotation );		D3DXQuaternionSlerp( &InterpAnimJoint.Rotation, &BeginAnimJoint.Rotation, &EndAnimJoint.Rotation, InterpValue );		//D3DXQuaternionNormalize( &InterpAnimJoint.Rotation, &InterpAnimJoint.Rotation );		D3DXVec4Lerp( &InterpAnimJoint.Position, &BeginAnimJoint.Position, &EndAnimJoint.Position, InterpValue );		D3DXVec4Lerp( &InterpAnimJoint.Scale, &BeginAnimJoint.Scale, &EndAnimJoint.Scale, InterpValue );	}