I'm trying to start my Mac in Start Up Manager but no matter how many times I hold down the Option key during start up it just won't go into the Start Up Manager and reverts to a partition that i don't want to start up in. I went into System Preferences and to Startup Disk chose my 2nd partition to try to get into then hit the restart button and I get a pop up window responses of "You can't change the startup disk to the selected disk. The bless tool was unable to set the current boot disk." What is a "bless tool" how can I get this to accept the partition change? I hope its not complicated, any suggestions?