The experts around this community site typically knowledgeable about Mellanox products. this is a Flextronix product (not made by Mellanox).
googled this switch model found the following: http://www.ibswitches.com/Docs/Flex%2024%20Port%20Users%20Manual.pdf
From my experience, things like this happen when: the cable pin-out is not correct, the serial connection rate is not correct or things around this area. checkout the user-guide for the connection details..
good luck.