If you were (for any reason) trying to remove and redeploy the Exchange Server 2007 on one node in an Active/Passive cluster, and when finished tried to failover the group to the next node and you got something like this in the Application Log:

Source: MSExchangeIS, Type: Error, EventID: 5000
Description: Unable to initialze the Microsodft Exhcnage Information Sotre service. Failed to find the working directory parameter from the registry – Error 0x80004005

Then just check the registry (exactly as the message told you) and find the differences under the HKLMCCSServices<theservicewiththeerror> and compare it to the working node in the cluster. You’ll find a missing string value (REG_SZ) named: Working Directory

And the value would be something like this: C:Program FilesMicrosoftExchange Server\MailboxMDBTemp

Now if this didn’t solve your issue, use a registry tracking tool to find the differences