[c-nsp] 3750 stack slave switch replacement

[Pete S.]

Make sure both of your 3750's are the same IOS version.
As Asbjorn stated its most likely a stack incompatibility, usually
because of differing versions.  If the minor release is off by a few
revisions, the slave normally comes up, gets the new code and works
fine.  Otherwise you have to upgrade it manually before you add it to
the stack.  Make sure they're both the same feature set also.
i.e. You don't want the master, doing ospf,  to fail, and have the
slave running ip base(no ospf) code to pick it up...