Visual Web Developer Express DataClasses.dbml error "The operation could not be completed. The parameter is incorrect."

The only thing I've found in searching this link http://forums.asp.net/t/1298084.aspx/1 which unfortunately concerns VS 2008, and I am working in Visual Web Developer.

If anyone has seen this error before I'd appreciate any insight.

I've tried closing and reopening the project, as well as checking the compiler errors.

EDIT - I don't understand why this post is getting downvoted, if it's because I've been stupid about something then at least enlighten me to how I'm being stupid so I can learn.

I've tried editing the DataClasses.designer.cs but as I expected that hasn't had any effect. I've checked the Dataclasses.dbml in other projects and they st开发者_JS百科ill open correctly, but in both my development copy and backup copies (backups of the live and the old dev) for this project it doesn't open.

Have you tried deleting the DBML file and recreating it? I've seen where the database mappings can get corrupt and usually just recreating it has worked for me in the past.