pylon:
You should post the sketch version that generates the errors in the SCADA. Does your SCADA support ModBus RTU or ModBus ASCII?What kind of Arduino are you using? The wake up process needs some time. Does your SCADA send the message again if the Arduino is too late to receive it (that would be against the ModBus specs).
My SCADA supports ModBus RTU, ASCII and TCP/IP, I'm using InduSoft (don't know if you know the software). And I can make the software to send the message again if I want.
Sometimes I also get a problem that is something like "rx char timeout" or something like this, it depends on the sketch that I upload. But the one that I'm developing the most is the one that i posted in the first 3 comments.
Thanks for the help
Dm