Monitor serial blocked when using pl2303 usp to serial adapter

Hello

Why have an Arduino Pro Mini 328 and a usb to ttl pl2303. Schetch was successful uploaded to Arduino but, when I choose "Monitor Serial", to see somes "Serial.println" in my code, the monitor serial is blocked. A message tell me that "COM4 is busy" - COM4 is the port where the Windows reconized my usb adapter.

Can I use monitor serial with Arduino Pro Mini or it is an issue?

It should not be an issue with either the IDE or mini.

Just hooked one up here to try and all works fine.

Maybe its in your sketch or wiring ?

Could you provide the sketch and a schematic of what you have hooked up.
Also try the example serial read without anything hooked up to the mini.