You have battery patch installed. It's the only thing that sets the lower limit to 125Mhz (unless you did so by hand, but then you'd know that...) Please go to the battery patch thread for help with that.

Reality: You do not want to use 125Mhz. It's unstable, can cause slow wakeups (missed calls), and saves almost nothing over using 250Mhz as the base. In fact, there are good arguments to be made for setting the min to 500Mhz, as it's the most efficient when it comes to cycles of work per mAh.