WELLINGTON, New Zealand (AP) - A computer glitch believed caused by work on telephone lines linking radar systems blocked air traffic controllers from properly monitoring scores of aircraft over New Zealand. Controllers spent more than 90 minutes Wednesday using a backup system to guide the planes to their destinations. Authorities were investigating the system failure, but stressed it was not an early version of the Y2K computer bug. Heather Hayden,  spokeswoman for Airways Corp., the company that controls New Zealand's air traffic control system, said radars were operating but were not able to communicate with each other, meaning there was no nationwide picture. Flights were delayed throughout the country while different air traffic control centers kept in contact by telephone to discuss aircraft movements.