What avast version are you using the “Avast Sandbox” is only in paid versions (also the latest regular release build is 2015 10.4.2233) ?.

I wouldn’t have thought that you would want MS Excel running in the “Avast Sandbox” - if you open the “Avast Sandbox” check and see if Excel is listed to always run in the sandbox, if so uncheck it. Or try resetting the “Avast Sandbox” back to defaults.

Sorry I can’t be more helpful, but I use avast free without the “Avast Sandbox.”