I got the same error message. I had installed 3.0 be transfering it directly into my web server, and installed from there. Then I went to load the files in my computers local website and tried to connect my database using the database connection string. then got the error message. So i stopped the computer install. but when I went to my website in the admin section the topics menu had doubled up on all the topics. I reinstalled my database from a backup from the server and all went back to normal on the website.
I am going to try connecting to the local host database computer to see if I get the same error.