MOSS 2007: Adding document to document lib results in error “Item Does Not Exist” when checking in

We are testing out our SP site on a staging environment (we do have access to hive logs, but haven't had much help with them) and we're getting a very strange error that doesn't show up in our dev environment.

When uploading a document to a document library (these are doc libs created with a custom content type), after filling in the properties and clicking check in, I get an error "Item does not exist The page you selected contains an item that does not exist. It may have been deleted by another user." I cannot figure out why this is happening, and it can't be replicated in the dev env.

Weird 'workaround' that we figured out to force it to check in.. after getting the error page, click back to go back to the edi开发者_运维技巧t page, refresh the page, then check in. This works every time without error.

Another note, it seems to only happen after a document has been added recently. The first document added to the lib always checks in perfectly fine, but always the 2nd or 3rd document will get this error. After that it has a high chance of happening.

Any clues? We have an older code base (which honestly isn't all that different) on our production server that works fine, and the staging and production environments are identical.

The error seems to occur during the EnsureItemIsValid() method according to the error stack trace (which occurs at some point during the SaveButton.SaveItem() method). We have an ItemUpdated event with this content type, however it appears to be getting through that just fine.