I believe that this error occurred upon upgrade to 10.3.1 on Jessie, but I am not sure about that. It appears that the desktop file in raspi-ui-overrides was not updated and still referrs to 10.0. My fix is to run in Terminal:
I experienced a similar problem bringing up a RPI2 for a friend; the toolbar ‘Mathematica’ button stopped working after updating and upgrading an Element 14 Noobs + Recovery micro SD card (SK 40522 71053). Curiously, my own RPI2 SD card, derived from a ‘raspian-jesse’ image download dated 2015-11-21, worked fine after the update/upgrade.
Inspecting the file “/usr/share/raspi-ui-overrides/applications/wolfram-mathematica.desktop”
from both RPI2’s suggested the following fix, which solved the my problem:
Change following lines to match the file contents seen after the “raspian-jesse” SD card update/upgrade:
TryExec=Mathematica
Exec=Mathematica %F
The changes were made from a command line terminal using the ‘nano’ editor:
cd /usr/share/raspi-ui-overrides/applications
sudo nano wolfram-mathematica.desktop
One could also use “sudo startx” at the command line interface prompt to run the GUI with root privileges, then navigate to “wolfram-mathematica.desktop” using the file manager, then make the required changes using the text editor. To revoke root privileges, exit to the CLI and restart the GUI using the regular ‘startx’ command.