This is same exact problem I am having on 360 when starting a 12 team public dynasty it always gives me the same error when validating the roster. I am using the pastapadre roster. I also have a friens that gets this erroe as well on his system. I will check and see if private will help me start it. updates coming soon.
P.S. If anyone knows the fix please PM me asap! EA is driving me crazy
Thanks
UPDATE: after turning the setting to private it started fine, you can then turn it back to
public in the commish menu after it loads.I do Still think that EA should look into this and
maybe a patch can fix it.