I'm getting the following error on the admin beginner trail; create and share a dashboard in the reports and dashboards module: There was an unhandled exception. Please reference ID: HCOAKAFC. Error: Faraday::Error::ResourceNotFound. Message: NOT_FOUND: The requested resource does not exist.

I went through other posts that reported the same error and most reference the presence of a namespace. I'm using a new org with no namespace registered so am not sure what the cause is. I'm wondering if it's related to the fact that I can't access the chatter tab in this org. I keep getting a data access error to the reocrds I'm trying to merge every time I click on the chatter tab. 

Anyone Seen this on the validation rule trailhead? - Challenge not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, Contact Must Be in Account Zip Code: []