An issue with unresponsive task items has been reported on some Windows (7 and 8 primarily) machines. In these cases, it seems that the in-program videos are causing errors after playback.
As of version 9.0.9 of Symphony Math, these issues can be resolved by clicking the Settings icon at the top right of the screen (the gear icon). Setting Visual Effects to the lowest value (slide to the left) will deactivate all HTML5 videos in the program. This settings change should prevent unwanted task freezing.