One of our users got this error when he tried to post something on his SharePoint 2013 newsfeed:
Microsoft.Office.Server.Microfeed.MicrofeedException. Internal error code: 28

We all have a love/hate relationship with the cryptic Microsoft error codes, but this one is very annoying as it doesn’t say anything!
This error pops up when your limit for your mysite is reached. Empty your recycle bin to free up some space.
In this case:
https://your url/my/YOUR_ID/_layouts/15/RecycleBin.aspx
https://your url/my/YOUR_ID/Blog/_layouts/15/RecycleBin.aspx