unable to diable a netword connection :(

While trying to disable one of my network connection, I get a message
saying that "it is not possible to disable this connection now. this
connection may be using one or more non plug and play protocol, or may
has been initiated by another user or by the system accout".

well... there is only two users on this machine, mine and the
administrator and none can disable the connection. the connection only
runs TCP/IP and QoS.

I always was able to disable this connection and suddenly I get this
error where am I wrong ?

please, help!

TIA,
Pierre.