Hi
some possible solution for that issue:
- your "default" Users have no execute rights for the codeunit, make sure that every user can execute all important codeunits, as an example use the access groups of the cronus company
- your licence is not for the installed NAV Version (maybe you have update from an older Version to 2013 - you need a complete new licence file)
This two points are both happend in our update process from NAV 2009 to 2013