You cannot launch Maelstrom.exe by iteself, you must use a shortcut where the "Start in" property points to the ERAS mod. This way, you can play several different mods, like COAS, GOF, etc., with the same Maelstrom.exe.
Now that you know the path to the 64 bit Maelstrom, go back to that shortcut (in the directory above, which looks to be C:\Gry\Maelstorm\gentlemen-of-fortune-maelstrom-engine), right-click the ERAS shortcut and change the Target to: C:\Gry\Maelstorm\gentlemen-of-fortune-maelstrom-engine\DirectX9_64bit\Maelstrom.exe
Then change the Start in to the path where you put the ERAS files. Click OK, then use that shortcut to launch the game.