If you get a message referring to a null (eg invalid use of null) the first thing to check is if there is a blank record in one of the databases, particularly  one you have recently edited.

If you are not able to fix this problem yourself, send the file pnw.mdb (from c:\polesnwires) to support@ipowermation.com.

This error does occur in version 6 and should not occur in version 7.