User does not exist or is not unique

I am not able to add a fba user to the site collection permissions.  Someone can request access and I can approve the request, they receive the email with temp password and then change their password.  But when I try to add the user to the site collection permissions, the formsauth name comes up in the people picker but when you click Ok, I receive the "user does not exist or is not unique."  It does take at least a minute for the peoplepicker to find the user.  I am able to to add AD users to the site with their windows authentication and do not get the error.  I also tried adding the role to the site rather than the user and I get the same error.  Any suggestions you can provide on this issue is much appreciated!

I would guess that there's an issue with your FBA setup. Likely it's correct in one or more of the web.config's, but not in all web.config's. It will need to be setup in the web application that you're using (as well as any extensions/zones that have been created for that web application). It also needs to be setup in the Central Admin web site and the secure store web service.