Jeff, i understand, as I had as I had a similar problem, but with two sets of Shimano pedals. Had 2-year old pedals on one commuter, and brand new pedals on another commuter. But I couldn't clip out of the 'newer' pedals, without major fussing and (on occasion) swearing. Found out that Shimano has 2 cleat styles, a SH 51 and SH 55. The 55 is the older style, and they are pretty cranky when used with the newer SPD pedals.