You're almost certainly right that not including your last boss as a reference is causing a problem with prospective employers, particularly when a job is one you've held for a good amount of time, as you have. Typically, the most recent job(s) are those which are most important for reference purposes, so if your only references are from 10+ years ago, they are unlikely to be useful. After all, a person may have a stellar reference from 1998, but what has s/he done lately? Imagine what a person could have be up to in 10 years – both for better and for worse. So having an old reference is not a problem, but having all old references is a problem.