Hi Roberto
It may be a problem with autonegotiation. Although there is no errata for the M5223X available I believe that it has inherited a EPHY bug from the NE64 - see the NE64 Errata MSE9S12NE64_1L19S.
You can also download the following code to your eval/demo board to be sure that it is not simply a software issue - the software lets you browse, telnet and ftp your board and is set to autonegotiation as default - you can change the settings using a telnet menu is you wish and load your own web pages via FTP:
http://www.mjbc.ch/software/uTasker/M5223X/uTaskerV1.2beta005_m5223X.s19
It is a demo project for the uTasker operating system with integrated TCP/IP stack. See http://forums.freescale.com/freescale/board/message?board.id=CFCOMM&message.id=274 if you would like more details or play with an on-line demo. It is free also for non-commercial work.
The EPHY bug is a bit of a nuissance since not all switches, hubs or PCs will be able to autonegotiate and the only work around is to set the speed without autonegotiating. It is unfortunately an argument for avoiding the M5223X in favour of a device with external PHY but then again it is something which you can live with in many circumstances.
Regards
Mark Butcher
www.mjbc.ch