HU locked by the system

Hi Gurus,

We have a problem with a handling unit locked. When we try to confirm the transport order associated or start the post goods issue of its delivery, we always get the message:

HUGENERAL 053 "Handling Unit can't be changed".

We looked at HU03 and in the "status" tab we can see the following information for the System Status:

LOCK Locked

PHEX Phisically Exists

WHSE In Warehouse

We tried to unlocked this HU with no success... hopefully you can light our way.

Thanks in advance,