after installed VirtualBox in my Openmediavault which version is 4.1.12, but I cannot create VM as 64bit, only 32bit can be choose.

hi,
I cannot create VM as 64 bit in VirtualBox which installed on my openmediavault, I checked my cpu is 64bit and my openmediavault software is 64bit, but when I created VM in virtualbox, I cannot find the 64bit OS, I don't know why, please help me to find the solution, thanks!