Intermittent login script failure.

One of the businesses my company provides support to has recently changed the user logins from personal name based to position based ie the sales manager now logs on to the NT4 domain as sal00. All the workstations are running NT4 with service pack 6a. However, since the changeover, some of the staff’s login scripts do not process, leaving them without mapped drives etc. Is there a way to force the login script to run every time?