Microsoft Business Solutions Navision 4.0 was released in 2005. NAV 4.0 SP1 follows later the same year including Navision Employee Portal as a replacement for the Navision User Portal.
Same year Microsoft announces Navision 5.0 as the version with a completely new user interface to be released in late 2006.
Microsoft again changes the brand name in 2005. This time from Microsoft Business Solutions to Microsoft Dynamics. At the same time the name Navision is changes to NAV (not nav but n.a.v. - with all letters pronounced).
In 2006 an delayed Microsoft announces that the new user interface will not be part of Navision 5.0, but instead it will be released 6-12 months later as Microsoft Dynamics NAV 5.1.
So when version 5.0 was released in 2007 it was without the new client, but it did have many new application features such as a completely redesigned Job module. The job module had basically not changed since the release of Navision 3.01 (the character based version in 1990).
Again in 2008 Microsoft announces delays. Navision 5.0 SP1 is released without the new client. The new version including the new client will be called Dynamics NAV 6.0, but released in 2008. Just a few months later they announced that it would be called Dynamics NAV 2009 and be released in Q4 2008.