You need to be sure that you have the same mypaint as mypaint-data. I ran into that problem. I updated via app manager and it didn't update the mypaint-data so it wouldn't launch.

Aapo gave the codes on how to tjek that in xterm on page 18 i think.

If you updated to the newest maemo8 then you can get the mypaint data here
http://maemo.org/packages/view/mypaint-data/

and then do this in xterm as sudo gainroot:
code in xterm:
cd /to/where/file/is/located/ "enter"
dpkg -i mypaint-data_0.8.2-1maemo8_all.deb "enter"

It worked for me and it seems to be working fine. Takes some time to load more than the 0.7.1

e: Will try to get back soon with info on the new version when i have the time to test it