We use Moodle open source course management system developed originally in Australia. By default the spelling for enroll was enrol, which is used in Australia, and according to several English dictionaries, is also acceptable. We've modified the default language to be American English; so for new accounts, you will see no problems; however, if you signed up to Cognitive Class before this change was made, you need to correct this by updating your profile on our site. Please go to:
Settings » My profile settings » Edit profile » Preferred language
and choose American English for the change to take effect.