Sometimes the method stored on the actual GC, not the software, can become corrupt. It may cause you to see strange, nonsensical errors. In this case you may need to clear the local memory, and reset the GC to the default settings, while preserving the ip address and the configured inlets and detectors (things configured as AUX may need to be reconfigured).
To reset the memory, turn off the GC. Hold the Clear button, turn on the GC while still holding the Clear button. Continue to hold the clear button until the GC powers on completely. Memory reset complete.