Hello,
The attached file is a published file, which cannot be open or edited in GWD. Could you also attach pre-published source files?
Could you also try to clear the cache and re-launch GWD to see if the problem still happens?
Linux /usr/local/google/home/<your user name>/.local/share/google-web-designer/data/cache
Mac /Users/<username>/Library/Application Support/Google/Web Designer/data/cache
Win C:\Users\<your username>\AppData\Local\Google\Google Web Designer\data\cache
Thanks,
Mariko - Google Designer Team