Sorry for the trouble jthibedeau, but sounds like you're going to have to troubleshoot it in the field. You may have to write a simple troubleshooting program and start pulling other modules out of the base and/or move the H2-ECOM100 to a different slot. I recommend you put an END at the top of ladders, then insert your test program above that, which simply does a LD, LD, LDA, RX/WX and see if you can get that to work in the field. If it doesn't, change one variable (i.e. power down, remove one module, power up and try again, etc.) It could be that another I/O module in the field is interfering with the base (inducing noise, who knows), or it could be a power budget thing, dirty power, etc. SOMETHING, of course, is different if it works in your lab but not in the field. Therefore isolation of the issue is necessary.