If the build fails in a way that doesn't make sense, such as after you update DX, hold Shift and select the Play button on the toolbar. Diorama64 deletes the files from earlier builds and builds the mod from scratch.
If you're stuck, ask in the #diorama64 channel on the Star Haven Discord server. Say what you were doing and what went wrong, and include Diorama64's log, which Help > Open Log File opens.
If you've found a bug in Diorama64, report it with Help > Report a Bug.