We are having trouble getting a DSS 4450 working off of a 7424LD telephone at a customer site.The extension number 500 is set up as an operator on the 1st port.I have programmed the 3 pages for exts 100,200 and 500 and also have put ext.500 in ext status.Am I missing something?When we hook up the DSS it causes the phone to cut out and the display flashes off and on.Any help would be greatly appreciated.Highwood