This is caused by an obscure OSCAR bug.
To solve it, enter the "Preferences" window:
Then find the "Length of link and form names to display on appointment screen" field:
This sets the number of letters shown for each eForm name on the schedule screen and blows up the screen (for some reason) when it's zero. Change the number to at least 1 (2 is usually a good number here) and the schedule should go back to normal.
Click "Update" when set to ensure your changes are saved.