Google says my feed was "disapproved" but they didn't provide a reason - what should I do?

First try logging into your Google Merchant Center and clicking on the data feed name. Google will often post the reasons for rejecting a data file here. If there are no specific reasons listed, use the following link to contact Google to get some information about the feed.
http://base.google.com/support/bin/request.py?contact_type=error&ctx=direct

Google is usually very good about sending a reply, but keep at them if you don't hear back within a couple days.