Well I'm having my own problems with the installation but I'll offer some of my lessons learned. I can't guarantee anything I say at this point.

You might find, as I did, that you are defaulted to a single master database that uses, for example, YOUR id as it's name. The yabbse install scripts will then go ahead and create all the required tables in that database. The error message you're reporting leads me to think that is the problems you're encountering. To check it out simple put your id as the database name rather than yabbse and see if the install proceeds without that particular error.