First use: "Cannot execute DROP TABLE IF EXISTS civicrm_relationship: DB Error: constraint violation"

With Joomla 1.0.13, I installed CiviCRM 1.9. It worked mostly, but when importing contacts, at the last step it failed and sent me to the login screen. A search of the forums revealed that the problem is known and fixed in 2.0 alpha. So I uninstalled 1.9 via joomla, then installed 2.0a. After increasing disk quota and memory use, it installed fine. But, upon first use, even when going to CiviCRM Home (from within joomla), I get this error message:
"Cannot execute DROP TABLE IF EXISTS civicrm_relationship: DB Error: constraint violation"
A search of the forms found only one mention of this, but no one responded to it. So I am assuming it is a 2.0a bug.