changed blog URL – now ERROR 500

Hi everyone,

First of all, thanks to all who will be able to help us.
We got an issue on our website. After changing WordPress address URL of the blog to http://www.imexade.fr, the site is still available for navigation but not available to login with user name and password (users and admins).
The error result code is “Error 500 – Internal server error
The server encountered an unexpected condition which prevented it from fulfilling the request.”

public Website URL: http://www.imexade.fr (domain name)
defalut URL: http://francais.imexade.com

We tried to rename and change “plugins” folder as explained in other topics and tried to change “.htaccess” file on ftp server.

Thanks for your help!!