ciscoMgmt is from the CISCO-SMI MIB. ciscoBusMIB is from CISCO-BUS-MIB. Noet that evey MIB has some pre-requisite MIBs defined under the IMPORTS section of that particular MIB that must be loaded first, other wise you'll see errors. Meaning that there's a specific MIB Loading order that must be followed. In your case the error indicates that CISCO-SMI MIB must be loaded first. This is true for all MIB loading/compilation.
Have a look at http://www.cisco.com/warp/public/477/SNMP/mibs_9226.shtml that talks about this in more detail. Especially look at the sections 'What Are the Minimum or Pre-requisite MIBs that I Need?' and 'MIB Compilers: What Are They? Do You Care? What Issues Might You Encounter and What Are the Workarounds? and '1. Load ordering: ' in the above doc which should clear this up for you.
