The New expiration_date attribute causing you problems ? post I published in May 2007 was created when the expiration date attribute was first implemented by Google Base.  Although I do still follow this for some of my feeds that I have been running for years and don’t have any problems, others have been experiencing and reporting errors.  I believe that Google Base has made some changes surrounding the requirement of this attribute.

In reality unless you want the item to expire before the default (e.g. for products its 30 days) you don’t even need to include this attribute.