Ok that error makes it more clear.
The icon on server is not there where it was before.
Icon/avatar was deleted or permissions on system have changed and user can not read the folder.
Clients who see the icon/avatar have it in cache. The client does not ask the server then.
You do not have it in cache and your client asks the server for the file but server can not deliver it. This is way you get the error.
Short
