Upgraded to the 4.7 version. Our site runs the brave theme (https://invisioncommunity.com/files/file/8063-brave-ipsfocuscom/), so getting warnings that we need to update the theme after upgrade is normal. Typically we can still access the interface and change to a default theme, upgrade the theme and revert back to using it. I did verify that the theme has an upgrade available once we are on 4.7 we would go to the marketplace and upgrade it. This time upon completion of the upgrade both the ACP and basic site generates 500 error. 

PHP error log shows:

 mod_fcgid: stderr: PHP Fatal error:  Cannot use "parent" when current class scope has no parent in /home/prod_ak501st/ak501st.com/forum/system/Theme/Theme.php(2703) : eval()'d code on line 45

Any ideas how to get back to a default theme without ACP?

Ran Recovery mode and was able to successfully get back up and running. Ironically was not the default theme it was the Widgets Extension that caused the issue.

 

Glad to see you managed to get this resolved. Please ensure you report the issues to the author 🙂