1004 Host error

I'm new to this site, hope I'm in the right spot. We have 2004 Hendrick 20zxg-1326bt-atc5 router and we are getting a 1004 Host error at start up and we can't find why what or why we are getting this error. We believe this is a communication error, but don't know what is causing this or how to clear it. We have tested all of the controls/ drives and they all seem to be responding. We believe that the PLC is operating based on some tests that we have done. We have changed out the control board and checked the comms. everything seems to be correct. We are wondering if anyone else has experienced this problem. Thanks.