c-set-style not working in 21.1

[Mickey Ferguson]

I am running emacs 21.1 on NT 4.0 and c-set-style doesn't work.  I have
(c-set-style "stroustrup") and when I execute it, it returns with an error
message of "c-set-offset: Offset must be int, func, var, vector, list, or in
[+,-,++,--,*,/]".  It used to be fine back when I ran it on emacs 20.6.

It looks like maybe I need to execute this only after a C or C++ file has
been loaded.  So maybe that means that I need to load some library before
executing this statement.  Any ideas here?