This is more a note to self which will hopefully help someone.
The last couple of weeks I have been working on a web application that uses WCF Data Services (oData) and jQuery. I started receiving the following error: "The etag value in the request header does not match with the current etag value of the object.". After hours of struggling I found out that it was the oninsert trigger in my database causing the problem. It seems that when you insert the data the trigger changes that and then it is different from what you inserted and it then throws an error instead of returning the record you have just inserted.