Sorry - I didn't catch that 4 of your 6 users were working. Though, I still think it could be worthwhile to see if their device and service is working.

Some ideas:
At any rate - has it worked for these 2 users in the past?
Are these users able to browse external sites on a desktop computer?
Do these users have different policies on their devices vs other users?
If you active the user on a completely different device, does it work then?
You could also try re-registering with the wireless network:

since I can't post links yet...

To register a BlackBerry smartphone over the wireless network, complete the following steps:

1. On the Home screen, go to Options, or click Settings > Options.

Note: The location of the Options screen depends on the BlackBerry® Device Software and theme you are running on your BlackBerry smartphone.
2. Complete the step associated with the BlackBerry Device Software version you are running:
* If you are running BlackBerry Device Software 4.1 or later, click Advanced Options > Host Routing Table.
* If you are running BlackBerry Device Software 3.7.1 to 4.0.2, click Host Routing Table.
* If you are running BlackBerry Device Software 3.0 to 3.7, click Network.
* If you are running BlackBerry Device Software 2.0 to 2.7, click Network Settings.

Note: Some BlackBerry smartphone users running BlackBerry Device Software 3.7.1 might find the Register Now option on the Network screen menu.
3. Display the menu and click Register Now. Your BlackBerry smartphone connects to the wireless network.





I doubt it's the case, but it could be worth checking to see that the browser service book exists ... If it does exist, it could be corrupt in which case your BES admins would have to re-push them.

look for KB03151 on blackberry's website.


Hope this helps...