Thanks. I double checked all of these, tested that mirror lock is ok with a 2s settings. Checked forced bulb. Started well, the "shutter release port" field disappears, which sounds good.
Then tried a 1s exposure (with force bulb so should trigger what is needed) but ot no avail though it started well, invoking eosremoterelease, but insist on communicating to that
damned shutter port :

18:17:57.897: [INFO] Starting 1 seconds exposure (+1 seconds mirror lock).
18:17:57.897: [DEBUG] Starting exposure (exptime: 1 secs, mirror lock: 1, force bulb: true, exposure index: 0)
18:17:57.897: [DEBUG] Mutex locked
18:17:57.897: [DEBUG] Setting exposure widget bulb index: 0
18:17:57.897: [DEBUG] Setting radio/menu widget shutterspeed: 0 (bulb)
18:17:57.897: [DEBUG] Setting new configuration OK.
18:17:57.897: [DEBUG] eosremoterelease Mirror Lock for 1 secs
18:17:57.897: [DEBUG] Setting radio/menu widget eosremoterelease: 2 (Press Full)
18:17:57.897: [DEBUG] Setting new configuration OK.
18:17:57.897: [DEBUG] Setting radio/menu widget eosremoterelease: 4 (Release Full)
18:17:57.897: [DEBUG] Setting new configuration OK.
18:17:57.897: [DEBUG] End of mirror lock timer
18:17:57.897: [DEBUG] Opening remote serial shutter port: 7623 ...
18:17:57.897: [ERROR] Failed to open serial port: 7623
18:17:57.897: [ERROR] Error starting exposure

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