I have a slightly different problem.
After upgrate directly from 4.5.5 to 5.0.2 everything is working but Admin interface is very slow to load when zimbra_posixaccounts and zimbra_samba zimlets are deployed.
I still CAN login as a Domain Admin user as well as a Zimbra admin user who does not have posix/samba account. But the picture is the same. When a browser is reloaded Admin interface can be accessed. When I log out and log back - the browser (Firefox) hungs with this message in the status line:
Loading script:/zimbraAdmin/res/zimbra_posixaccount.
js?v=080130223433
If I then go to Advanced preferences and clear the cache - I am able to load the Admin interface again.
Since as I mentioned, I am able to login to Admin interface as Domain Admin, this is not exactly the case of the discovered bug.
I wonder, if the fix in 5.0.3 also address the above problem?