Reaktor and other Native Instruments do not currently support multi-client use in OSX; Therefor e, they will not work in another user account (other than the root user). This is a part of Native Instrument's copy protection scheme. These applications allow for two authorizations per license. The only way to fix this would be to install under each user, however, this would require multiple licenses.
There is currently no "workaround" for this issue. Native Instruments is developing an "Educational" version for schools and other institutions that require multiple accounts on one computer to have access their software. No release date has been set, but is expected soon.

This applies to Reaktor, Reaktor Session, Absynth 2 and Kompakt.