When trying to migrate my gems from rubyforge to gemcutter I got the following error :

GarysMac:yore gary$ gem migrate yore
Starting migration of yore from RubyForge...
A migration token has been created.
Uploading the migration token to buzzware.rubyforge.org.
There was a problem uploading your token: disconnected: Too many authentication failures for buzzware (2)
Asking Gemcutter to verify the upload...
Gemcutter is still looking for your migration token.
GarysMac:yore gary$

I've seen this before with ssh on my Mac - it seems I have too many hosts set up in ~/.ssh/config, and unless it has a host setup that matches perfectly (or something) it gives up before trying all possibilities. I also seem to remember "IdentitiesOnly yes" to help in reducing the number of configurations tried.

Anyway, I debugged it by doing "rdebug gem migrate yore" and then "b migrate.rb:66" to debug the upload_token method.
When it got to the point of uploading the token, I used the token string it was going to upload, and by fiddling with ~/.ssh/config, eventually uploaded it myself. Then when I let the debugger continue, it succeeded. The following setting in ~/.ssh/config also succeeded with my other gems :

Host buzzware.rubyforge.org
        IdentitiesOnly yes
        User buzzware
        PreferredAuthentications password

Hooray!