Hi Danielle,
Are you by any chance on a Windows touch screen laptop?
If you are, please try this workaround:
Find the file “qt.conf” (probably here C:\Program Files\Animation Paper\qt.conf). Delete it or rename it (to save it). Then launch Animation Paper again.
This will force Animation Paper to use Windows Ink.
Let me know if this helped?
Cheers,
Niels