dmesg should show what the unknown symbol was. That's the correct kernel.
The code disables the a1 parameter when using a recent enough kernel version, so I guess you need to edit that check, but that's not your current issue if the module doesn't load.
The code disables the a1 parameter when using a recent enough kernel version, so I guess you need to edit that check, but that's not your current issue if the module doesn't load.