RT-AC87U - Cant create manual path media server, greyed out.

Hi All,

I'm having an issue with my RT-AC87U.

I want to create specific folders to share, however this option is greyed out, so I cannot use it.
I have done a factory reset - changed USB sticks, reformatted the USB sticks / external HDD's several times and used a different USB port.

It seems that no matter what I do, it stays greyed out.

I am able to share the entire contents on the USB stick, however, I just want to share some specific folders.

Any ideas?

Thank you in advance.