I have a master (5/05) with 14 slaves (5/03).
The master comm with DF1 polling mode.
I have a instruction "MSG".
The communication is good but after a few minutes, I lost the communication.
The led RS232 on the CPU don't flash.
I put the CPU on prog mode and Run mode and the communication go on.

Can you help me ?

Using Ethernet go online with the 5/05 and tell us if the MSg instructions are in error or enabled and waiting. This sounds like you are flooding the communications controller with messgaes and it cannot process them all. If you can post your ladder file / files it would help.

BTW are you using read and write from the 5/05 or reads in all 5/05 and 5/03's

I agree with Bob that it sounds like you are sending the MSG instructions too fast and filling up the SLC's buffer. Only posting your code will allow anyone to diagnose that.

For a system with this many slave devices, I strongly perfer to use "Standard Polling Mode" and use report-by-exception logic in the slave devices.

Tell us more about the system. Is it used principally for data collection from the remote sites, or for setpoint and command distribution from the master to the remote sites ?