Monitor menu always show "Serial port unavailable"

Windows 7 32bit. Arduino Pro Mini board, connected to USB port via USB to Serial breakout board built on the FT232RL FTDI chip. I installed Arduino Create Agent plugin, but unable to get serial port connected.
Monitor menu always show "Serial port unavailable". USB Serial port is active in Device Manager > Ports (COM & LPT) > USB Serial Port(COM9), driver correctly installed. I tried reinstall Arduino Create Agent plugin, driver, but none of this helped. I know this is very common issue around Arduino setup. How to solve this?

Try a different serial monitor such as Putty with the tx/tx of the 232 convertor linked together. ( see loop back) , to isolate the problem .
There are a lot of fake MAX232 converters around that die when you look at them.

I assume of course you've tried swapping the tx/rx connections around ...