Schengen Visas will not be stamped on passports issued prior to 2001. 20 year validity passports are being returned as the Bar Code is not visible.
Applicants who want a Schengen visa need to have 10 year validity passports, should be valid for 3 months beyond the duration of your extended stay & should have a minimum of 2 blank pages.
If your passport has a 20 year validity period & you want to travel to Europe, you will be required to apply for a new passport immediately