Does the arial.ttf file in the Fonts folder have a newer date than the
one in the System folder? Its presence on the Recent list suggests that
somebody tried to open the arial.ttf file, and maybe corrupted it in the
process. Assuming the arial.ttf in the System folder is older than the
one in the Fonts folder, I would delete the arial.ttf file from the
Fonts folder, reboot, and reinstall the font from the System folder.