I recently installed Gnome on my Dell OptiPlex 755 computer, replacing Ubuntu Unity. The computer (and most applications) now work, for the most part, but I now have a red ball with a white dash in the titlebar, indicating an error. The explanation of the error is:
An error occurred, please run . . . apt-get in a terminal to see what is wrong. The error message was Unknown Error (E: The package Thunderbird needs to be reinstalled, but I can't find an archive for it.)' This usually means (that) your installed packages have unmet dependencies.
I reinstalled Thunderbird, but received the same response from the terminal.
Why am I still getting the red ball with white dash error indication on my taskbar? My only alternative now seems to be to completely uninstall Gnome and start fresh, but for some reason I can't do that either due to this problem.