If you are trying to map a clip trigger, piano mode is available via Clip > TriggerStyle > Piano. This is because clips can be triggered with mouse, midi, osc, dmx and keyboard.
If you are trying to map a button, make sure your midi controller is sending Midi notes, and not Midi ccs (control change). Some midi controllers insist to send cc values from a button, while Resolume expects buttons to send notes.
From
https://en.wikipedia.org/wiki/MIDI#Messages
A MIDI message is an instruction that controls some aspect of the receiving device. (...) Examples include "note-on" messages which contain a MIDI note number that specifies the note's pitch, a velocity value that indicates how forcefully the note was played, (...) and control changes that allow adjustment of an instrument's parameters.