This blog posting applies to Microsoft Office SharePoint Server 2007.
I was still getting this error on one of my VPCs, and found some blog entries with a little difficulty. Thought I'd post another to make it easier to find. One thing is, there are two possible issues that are known to cause it.
If the machine you're running on is a Domain Controller, and you have installed MOSS as "Standalone," then you need to execute a fix to avoid the expired error. A standalone installation is one where MOSS installs its own database management system, and is not connected to an existing instance of SQL Server. A standalone installation will always have exactly one server in the farm, not multiple servers.
Microsoft has published a fix for this, available at http://download.microsoft.com/download/b/1/a/b1a6dceb-92a3-4808-8dac-b4e40c90ce00/StandaloneDCWorkaround.msi. Just download this and run it on the Domain Controller where you're experiencing the problem. (If you don't want to because this is a Domain Controller for your organization, why did you install MOSS on it, especially in standalone mode? Get a development server for that.)
Application Pool Identity
If you don't have a standalone installation, you may still get the expired error. This answer should fix that case.
The Identity used for your SharePoint site's Application Pool must be a Domain account with local server access. If you're using a machine account (such as local user, or NETWORKSERVICE), it may work under most circumstances but give the expired error for some operations. Therefore if you encounter this error you have to make sure you are using a domain account for the app pool identity.
Note, I've observed that the identity of OfficeServerApplicationPool keeps reverting to NETWORKSERVICE, so I can’t use this for my MOSS web application. Apparently this machine account does work for the Central Admin site, and SharePoint ensures that it's restored to this value if you change it.