I'm guessing that vanitygen is more strict or has different rules than production's Base58 rules.
Why are some of thse names marked not possible?
C:\vanitygen>oclvanitygen -k -o gpukeystestout.txt -i -f gpukeystest.txt -TPrefix 'mdemo1' not possiblePrefix 'mcoin' not possiblePrefix 'mBITname' not possiblePrefix 'mBITclear' not possiblePrefix 'mBITnic' not possiblePrefix 'mbotarmy' not possiblePrefix 'mdmzlist' not possiblePrefix 'maker7' not possiblePrefix 'makerofthings7' not possiblePrefix 'meventvwr' not possiblePrefix 'mdmzadmin' not possibleNext match difficulty: 5908459 (15 prefixes)