Today I tried to remove the user accounts from the Farm Administrators group, that have left the company a while ago. Unfortunately I was unable to do so, SharePoint presented me with an error 1387.
Using Google I ran into the following blog post Unable to remove user from SharePoint Farm Administrators group : Error 1387. Here Tim was talking about the fact that the accounts were deleted and SharePoint was performing some kind of check.
After temporarily recreating the accounts of the users, I was able to delete the accounts from the group successfully!