After solving the msExchVersion mystery, it has become apparent that even more of our Exchange 2007 users were unable to access OWA.
After logging onto the site, a very similar error is displayed: Exception type: Microsoft.Exchange.Data.Storage.StoragePermanentException Exception message: There was a problem accessing Active Directory. My first step was obviously to verify the msExchVersion.
After ensuring that this was correct, and that the users were still unable to use OWA, I had to do more digging. Deeper delving into this issue, yielded the following KB from Microsoft: http://support.microsoft.com/kb/949527
To use OWA the Exchange Servers group must have write permissions to the msExchUserCulture attribute. Easy to resolve, just allow inheritable permissions from the parent to filter to the faulty object / objects, as per the KB article.
Easy enough on one account, but if you had to change this setting manually on multiple accounts, you could use Set-QADObjectSecurity –UnlockInheritance to accomplish the task. For more information see Dimitri’s blog