Fatal error: Class 'modAccessibleObject' not found
This question has been answered by BobRay. See the first response.
The first message just says the MODX can connect to the DB server. At that point, it hasn't tried to connect to the database itself. On many hosts, MODX won't be allowed to actually create the database and assign a user to it.
In those cases, you need to create the empty DB yourself and create a DB user who has full rights to the DB -- then run setup. Make a note of the final user and database name when you're creating the DB because hosts will often add a prefix so the name is different from what you entered.
BTW, utf8 / utf8_general_ci is the recommended charset/collation for MODX. I always create the DB before running Setup just to make sure those settings are used rather then MySQL's dumb defaults.
