Error:
Sorry, Something went wrong ...The URL is invalid. It may refer to a nonexistent file or folder
Investigation:
Go to the SharePoint application server.
Open the Event Viewer.
See the details on the actual error.
e.g.
Database full error on SQL Server instance 'SERVER_NAME' in database 'SERVER_NAME_DATABASE_SITENAME'. Additional error information from SQL Server is included below.
Could not allocate space for object 'dbo.DocStreams'.'DocStreams_CI' in database 'SERVER_NAME_DATABASE_SITENAME' because the 'PRIMARY' filegroup is full. Create disk space by deleting unneeded files, dropping objects in the filegroup, adding additional files to the filegroup, or setting autogrowth on for existing files in the filegroup.
Reason:
The space/storage on the database server is either Full or permissions have changed on the server for the SharePoint Application.
Resolution:
In the event if space/storage is full, you have to check the size of database log.
Redefine the log storage limit using the application management.