I think after the lastest update I have a problem.
you got this error because you are trying to install wrong package. The theme file you supposed to install is betheme.zip
For more details about this issue, please visit https://support.muffingroup.com/faq/the-theme-is-missing-the-style-css-stylesheet/
Thanx you the stylesheet problem is solved. Only the widget area is blank. But i have a workaround for it.
So everything is fine now?
Is there anything else we can help you with?
Widget problem also solved. The plugin AIOSEO was the problem. They update it see here the changelog: New in Version 220.127.116.11
So thank you for your input and time ;-)