Uninstalling AVG Anti-Virus SBS Edition broke my MS Exchange

The licence for my AVG Small Business Server 2003 Edition recently came to an end and after looking around I decided that rather than renew it I'd replace it with Microsoft's new Forefront products. This is probably vast overkill, but I figured it'd be interesting to see how it all works and I generally prefer vast overkill anyway.

What I discovered was that it's quite an involved process to get all the various pieces installed and working (ever the way with 'Enterprise software') so I uninstalled the AVG software and for a little while now have been going without protection on this server. Yeah, yeah, bad idea I know.

Shortly after uninstalling I found that Outlook clients couldn't connect to the Exchange server on this box. Not only that, but people were getting bounce emails saying that their messages couldn't be delivered. Thankfully I route all emails through another external email server (with its' own anti-virus and spam filtering) before having them forwarded through to my internal Exchange server so I wasn't actually losing the emails, but clearly something was wrong. I tried the old 'restart the box' trick but even this didn't work so I turned my attention to the Event logs and started to look for any errors of warning. What I found, amongst others not seemingly relevant, were the following:

Event Type: Error
Event Source: MSExchangeFBPublish
Event Category: General
Event ID: 8197
Date: 19/09/2008
Time: 11:18:36
User: N/A
Computer: The server name
Description:
Error initializing session for virtual machine SERVER01. The error number is 0x8004011d. Make sure Microsoft Exchange Store is running.

Event Type: Information
Event Source: EXCDO
Event Category: General
Event ID: 8196
Date: 19/09/2008
Time: 11:17:13
User: N/A
Computer: The server name
Description:
Calendaring agent is stopping successfully.

Event Type: Information
Event Source: EXOLEDB
Event Category: General
Event ID: 101
Date: 19/09/2008
Time: 11:17:13
User: N/A
Computer: The server name
Description:
Microsoft Exchange OLEDB has successfully shutdown.

Event Type: Error
Event Source: MSExchangeIS
Event Category: General
Event ID: 9564
Date: 19/09/2008
Time: 11:17:12
User: N/A
Computer: The server name
Description:
Error 0x80004005 starting the Microsoft Exchange Information Store.
Failed to init VSERVER.

Event Type: Error
Event Source: MSExchangeIS
Event Category: Virus Scanning
Event ID: 9581
Date: 19/09/2008
Time: 11:17:12
User: N/A
Computer: The server name
Description:
Error code -2147467259 returned from virus scanner initialization routine. Virus scanner was not loaded.

What I took from these was that due to my uninstalling the anti-virus software Exchange was now broken because the Microsoft Exchange Information Store couldn't now start.

A quick google on 'Error 0x80004005 starting the Microsoft Exchange Information Store' led me to an Experts-Exchange post, and scrolling to the bottom informed me about a registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\VirusScan. I changed this, as suggested, so that Enabled is set to 0, restarted the server, waited a few minutes, started Outlook and held my breath. Very quickly emails started to flood in to their relevant folders.

Now all I have to do is get the Forefront products up and running nicely, and then probably upgrade my infrastructure to Server 2008 and Exchange 2008 (following the new branch office configuration).