How can I add usbip modules on Redhat 6 kernel?

Question

I have RHEL 6 with

# uname -r
2.6.32-131.0.15.el6.x86_64

I'm trying to build usbip modules on staging driver. Everything is OK. I have all needed *.ko files. But I cannot add those modules on running kernel.

# pwd
/lib/modules/2.6.32-131.0.15.el6.x86_64
# ls | grep ko
usbip_common_mod.ko
usbip.ko
vhci-hcd.ko

# modprobe usbip
FATAL: Error inserting usbip (/lib/modules/2.6.32-131.0.15.el6.x86_64/usbip.ko): Required key not available
# insmod usbip.ko
insmod: error inserting 'usbip.ko': -1 Required key not available

How can I add it? Do I need to rebuild whole kernel?

TIA, giobuon