PLC5 MSG Instruction to read from SLC 5

I programmed a couple of MSG instruction for a PLC5/80E to write and read data to a SLC 5/05 thru an Ethernet network on non-continuous mode. It worked during a long time, but unexpectedly stop working. Now, when the rung goes true, the Enable bit (.EN) and the Enable-Waiting bit(.EW) are set but the Start bit (.ST) never goes true and no Error is indicated. So .EN bit and .EW bit remaind set forever. However, when MSG instructions, write or read, are executed from the SLC processor, it works.
Please, somebody help me...

I use a timer to 'Timeout" the instruction if the ERR or EW bits are on for more then 10 seconds, I then set the TO for one scan to timeout that MSG from the queue. Then resume normal operation.