This exercise aims to explore the effects of climate change on wheat cropping systems. Firstly, the response of wheat to elevated CO2 is examined. Please be aware that as of version 7.4 only wheat, oats and barley are responsive to CO2 changes. All other crops will generate an error.
There are a number of ways to seek support for APSIM related problems: please see here https://www.apsim.info/support/support-2/. You may like to post questions as a github issue: https://github.com/APSIMInitiative/ApsimClassic/issues. Instructions on using github can be found here: https://www.apsim.info/support/support-2/github/.