When I try to access a link from our portal company website (SharePoint), for example AttendancePlaces/AllItems.aspx, it asks for admin credentials as normal but after that I get an error "Sorry something went wrong". 
In the log files, it says that the "Application error when access /AttendancePlaces/AllItems.aspx, Error the list doesn't exist with the current url.
I tried to access the list via SharePoint and says the samething (the list is the 1 that has 17 items and hasn't been modified by 15 months) 
It was working fine a few days ago, hasn't been modified in 15 months