Building for U7621-01-AX

I am trying to build for the UniElec U7621-01-AX, but I am failing. I tried the U7626-01 binaries but no luck. Does anyone know how to build for this particular router?

What's the error message?

I get a 'VFS: cannot open root device' during boot, and the device restarts.

Check the bootcmd param (assuming it uses uboot), it might be incorrect.