I feel frustration on behalf of us both. Remote debugging is a pain and considering that some 100,000 other installations seem to be working fine, the problem is probably on your site via conflict of some form.
Can you create a copy of the site so that we can work with it without disturbing clients?
query_posts, it's probably someplace in your theme. I do my best to ensure theme conflicts on testimonials widget plugin side are quickly fixed. However, it's up to the site owners to help me find them.
Please remember, you're getting paid by clients to support them. I don't think they or you are paying me. Therefore please be kinder in your responses.