Internal Instant Messaging Application

We are using Openfire and Spark at the moment.
It does a nice job, but we've been have issues where messages
don't reach their destination. We've had it for over 2 years now
and would like to switch to something different.

I was wondering if anyone has any suggestions?

Here's the requirements it must meet.

1. Integrate with Active Directory
2. The server must be on our network
3. Log chat history
4. Can be open source or commercial
5. Utilize MySQL or MSSQL
6. Be Vista and Windows 7 compatible
7. Can be installed or Linux or Windows Server 2003
8. Have a web client so it can be integrated on our website for customer support