Hi -
Here are a couple of things to check:
1. Did you upgrade your Unity Voice Connector for Microsoft Exchange 2000 to version 11.0(1) or later as part of your upgrade procedures?
2. Bridge licensing changed from version 2 to 3.0(3). Did you apply the new license file to your Bridge server?
3. To designate a 4.0(3) server as a bridgehead, you run the ConfigMgr.exe utility with the Create Bridge Account option.
4. In Unity 4.0(3) and later, there are new Bridge delivery location pages and new settings on the delivery location profile page. Remote Mailbox Length is one new field that must be coded.
5. In order for Unity subscribers to be able to send messages to and receive messages from subscribers on the Octel nodes with which Unity communicates, each Unity subscriber account must be configured with a serial number and mailbox ID.
Here is the link to the doc that references above items - http://www.cisco.com/en/US/customer/products/sw/voicesw/ps2237/products_installation_and_configuration_guide_chapter09186a008022fbda.html
Hope this helps!
Ginger