Using fieldpoint with scientific linux and USB-RS232 interface

I am using a desktop PC with SLC5 and an USB-RS232 interface. I need to program a fieldpoint FP1000 module within labView. Visaconf is correctly seeing the interfaces (4 ports: /dev/ttyUSB0 .. 3, mapped as ASRLx::INSTR, with x = 1..4), but when I try to use "Advanced Serial Write and Read.vi", I always get timeout. If I try "Optomux Send General Command.vi", it looks broken (the parameter "VISA resource name" is connected to the "port number" input of "FPOptoHandler.vi" and the type is not matched).

What am I doing wrong ? Am I missing some piece ?

Thanks a lot in advance,

Roberto Ferrari