I'm using Site Designer 3.0, Build 2873 on Windows 10 Home. When I try to open a .cgb file (from CSS Grid Builder), it gives the message "Checking backward compatibility" along with a spinner, and never gets beyond that. Does anyone have a fix or workaround for this?

I tried this and it will not open a .cgb file using 2873. Same message. I did however open the .cgb file in SD3 2815 and saved it. I then opened it in SD3 2873.

I cannot verify if everything is ok.....just that this process at least let me open a .cgb that was converted using SD3 2815.

Different Framework versions etc etc could have effects on the original file. Make a backup copy of you .cbg before trying this.

It ought to be reported to CC support that the current SD3 version cannot open cgb files. CC can't expect us to keep older versions of the apps just in case something doesn't work after an update.