Persistent problem upgrading 6.x-1.x sites to 6.x-2.x

I have tried a wide variety of approaches to upgrading a set of sites from the 6.x-1.x branch to the 6.x-2.x branch. I am also preparing documentation to submit once I get this done effectively, because I suspect others may have trouble with this. Currently I am stuck and need some help. I can get the 2.x branch to receive a login from a slave. In other words, the slave sends the credentials to the master. The master establishes the session with the UID in the session table on the master. I noticed there was no bakery_user entry created for the account, so I added it myself, entering the master and slave UIDs and the slave URL (just the root URL - tried both with and without trailing slash - no difference). All of what I am describing is only happening after adding the bakery_user table entry. Now, it redirects back to the slave but I notice very briefly on the slave that the URL cycles through a double slash bakery/login during the process (//bakery/login) and resolves to Access Denied. The slave session table shows only a UID 0 entry. What is most interesting is that when I return to the master site, the welcome message is queued in the session table and shows, and I am logged in. So, I am able to login to the master from the slave, but the session is not passing back to the slave. Thoughts? (The system works on 6.x-1.x.)