ArduinoMEGA uart1 doesn't work properly

Hello,

I'm a newbie on this forum but I have some experience designing and programming microcontroller-based circuits and I have a problem with the arduino MEGA. The UART1 RX interrupt seems to be died, I have tested the RX0,RX2 and RX3 pins and they worked fine, but this don't do its job. Anybody know if this pin is a special one, or it requires a special usage?

Thanks a lot!