If your pins are right in spec, then there's pretty much only two other possibilities for the issue. Those would be miscut keys or a non standard plug size. I would follow what Gordon said and measure out your keys to see that they are cut to the right depths and spacing. If they keys check out, then check your pin lengths and the plug diameter as well.
Depth and space information is here:
http://www.lsamichigan.org/Tech/SCHLAGE_KeySpecs.pdfThe Schlage plug diameter is 0.500" to my knowledge.
Best of luck sorting out the problem!