ProBoard.exe loads only Win32 plug-ins, and an x64 one only x64. Windows reports error 193 (“not a valid Win32 application”) when they are mixed. Keep one kind in the PEX folder..PEX programs from 16-bit ProBoard do not run. Use the .P3X version./I and then the plug-in's name. See Plug-ins.BBSLink, DoorParty and Skull Crash each need their own settings file with your credentials, and a connection out to the network. See Door networks and Ports.
Check the door's line in DOORS.PRO, the path to the drop file and the node's NODEDIR\NODE<n> folder. A door whose drop-file path changed between releases may need its command line edited. See Native Windows doors.
DOS doors run through PBLegacy and DOSBox-X. See DOS doors with PBLegacy.