Red crosses on mapped drives?

All my users on a small 25 user workgroup Windows 2000 server/Pro network experience red crosses on their mapped network drives if the drives are not used for some time. They can double click the mapped drive icon which displays the contents – but sometimes the red cross is still present. I have carried out the instructions from Microsoft KBA 297684 which details turning off the autodisconnect parameter on the workstations – but after a further 15-20 mins the mapped drives return to the red cross state – Any advice gladly welcomed.