Multisite login issue

I updated a few days ago and something seems to have gone wrong. I am running a multisite.

Anyone who now tries to login on a site gets:
“Invalid username for this site”

They used to be able to login on any of the sites so long as they were a user on any one of the other sites. Now the login seems to be site specific.

I have tried 2.52, 2.5 and 2.4 and have been running into the same issue.. So it might not be an issue with this plugin but I can’t see any other plugins that should be affecting it, at least none I’ve updated/changed in the last few days.

Any ideas would be much appreciated as this is unfortunately a very important feature of my site.

Christian

http://wordpress.org/extend/plugins/sidebar-login/