The issue is most likely on your target.
Assuming SMB/CIFS, does the system (Windows, Filer) know how to correlate the Centrify-provided identity with the user identity?
Remember: In express mode, the identities aren't in AD but emulated on the agent. You have to find a way to present this data to your target server.
Paying customers today use the LDAP proxy for these purposes.
Review this post since we've covered these types of projects several times: http://community.centrify.com/t5/Centrify-Express/Fstab-mapping-drives-difficulty/m-p/19960#M4122
R.P