login problem after upgrade

Hi,

I use the joomla's login form on a sidebar in my website.
After upgrade, my blogger and me are unable connect on the frontend.
I can connect (superuser) in my backend, but not my blogger (administrator).

I deleted his profil, and created an another. But the bug is the same.
Now, i cannot connect in the frontend too... and this is happened after the upgrade.
Do you have a issue for me ?

Thanks
Stephane