I have updated to 2020 R3.1 and when I load a project, the Xojo green "RUN" icon is not enabled? what have I done wrong? This means I am stuck with some large projects not being accessible for development and testing. Please help.
Which version ?
2020r3.1 doesnt exist
Do you mean 2019r3.1 ?
often when an old project os loaded the run button is disable because its set to run as 32 bit on a machine that only runs 64 bit code (macOS specifically)
Click on the macOS item in the navigator and see if thats the case