Some GPS units will not allow you to export to DXF but will allow export to GPX format which IRRICAD cannot import directly. The way around this is to convert the file to KML which IRRICAD supports and there are many free on-line converters such as "GPX2KML" (http://gpx2kml.com) or GPS Babel (https://www.gpsbabel.org/). It is a quick and easy process to convert the file to KML and import it into IRRICAD.
Tip: Make sure you only export the last survey from the GPS unit so that the file you import into IRRICAD does not span more than one UTM Zone.