Problem Connecting to Scanner

We have a G4 Mac, running OSX Panther, is connected to an HP 950PSC all In One Printer/ Copier Fax/ Scanner. Whilst it prints perfectly, unfortunately, for some time now, when requesting the scanner, we receive an error message “Unable to connect to HPAIO twain data source”. We have uninstalled and reinstalled the drivers, with no success.

Can anyone help as to how to resolve the problem?

Thanks in advance.