Markdovell,
Did you turn this customer into a KSU just so one person can answer incoming calls without it ringing them directly?
The error you have is showing correctly as busy since the Hunt Group is in control of the call and therefore it is busy and you are not allowed to take over the line manually.
The simple route would be to train the person to do a reverse transfer from the Hunt Group receiving the calls.
Give the user a DSS/BLF of the Hunt Group so they can dial 4, the default reverse transfer code, and press that button to answer calls ringing the Hunt Group.
You could also set the Hunt Group's [Group Call Pick-up Flag] if they just want to reverse transfer from one of the 3 stations, but this also allows them to answer any call directed to that station which is not ideal.
Hope that provides you with a better solution.
Thanks,
TE