From your screenshot, it looks like you at least missed "styles/admin.css". Could you have missed others as well?

This could very well be related to your file permission errors, which, as MarkS mentioned, is also related to why your cache is not getting updated.

As a brief refresher, upgrader documents were updated in February '17 with the release of 7.6.0, and can be found here:

Current developer of UBB.threads PHP Forum Software
Current Release: UBBT 7.7.4 // Work In Progress: UBBT 7.7.5
isaac @ // my forum @