Wouldn't say, it's solved. When I replace admin.smf.class.php I get
Parse error: syntax error, unexpected T_STRING in......../main/administrator/components/com_smf/admin.smf.class.php on line 1562
Well, I have the same "username already in use" problem. I want to use the bridge with J 1.0.15 and SMF 1.15.
I installed the component new, patched all files a few time new, no success. I searched this forum for hours, but couldn't find much about this problem.
It's not that I get always a blank page. It only happens, when I try to login with my sfm admin account. Each other account can login/logout correctly.
I'm wondering, if someone had the same problem and could solve it.

UPDATE: Looks like I could solve it by just deleting my SMF account name in the database jos_users. After that I logged in new with my SMF account. Done. And NO sync.