What you’re looking at in the output was the order of execution. Basically a list of steps that were performed before an error occurred. The most recent events are on top.
In this case the “error failed to open required” says the script was trying to load a cached theme file (specifically for the active user widget) but that it was not found.
As theme files can be generated on demand by clearing the system cache, a new set of theme files are generated.
Generally these types of errors are good for helping point you in a general direction. If you see references to things outside of the core IPB software such as hooks or 3rd party applications, you can discover if they’re interfering etc. Or in this case that it was a simple theme issue.