USB hub problem

Hello all!

I have an oldish monitor (Samsung SyncMaster 1200NF) which includes an
USB hub. On the back of the monitor there are two B connectors and two
A connectors. On the front there are two A connectors.

Now, when I plug the monitor to the computer (via one of the monitor's
B connectors), the "Generic USB Hub" is detected, there are four ports
available and one "unknown device" which makes the "USB device not
recognized" balloon pop up.

The monitor's on-screen menu includes an USB option which allows me to
select between A and B, although it doesn't say A and B what. It's the
first time I've used this monitor's USB hub, so it's not something that
was working OK and suddenly malfunctioned. The manual is not helpful,
it barely mentions the monitor's USB hub.

I'm guessing the four available ports are the A connectors, and the
unrecognized device is the remaining B connector. Why does it show up
like that? And why does the monitor have two B connectors in the first
place? This causes other devices plugged into the hub to malfunction
sometimes. What's wrong? Could it be a malfunctioning hub, or am I
missing something? I'm inexperienced with USB hubs so maybe it's a
newbie thing.

Many thanks in advance.

Diego