Re: phpbb3 -> bbpress converter
As I recall when doing this long ago, none of the users will work. You have to have them reset their passwords for their accounts to work.
On the keymaster account there was a trick to that which I do not recall at this moment. However, I do believe you can edit the database itself.
I believe it changes the role to admin instead of keymaster and then you will have to also change the password to something else.
Did you use the converter noted in this thread?
The first link I posted was a very good step by step process that could also give you the info you need.
If I find anything I will post here to further help out. Good luck.