Their (spellingcow) site is currently broken. Those of you noticing a DEBUG error when spellchecking should know that it is not this site causing the problem, but the debug error is on spellingcow's site.
I repeat **THIS SITE IS NOT THE CAUSE OF THE ERROR, and the error you are seeing is actually on their site.
I am thinking about removing the damned thing becuase this is the 2nd time it has caused problems due to errors on their site.
in the mean time, I am turning off the mandatory spell check for everyone. If you want it back on, go to your profile and turn it on.