Login/logout errors in Responsive Realestate

Problem occurred over night now

On internet explorer – I can’t log out 406 error
Internet Explorer cannot read this webpage format
HTTP 406

And On firefox I can’t log in – this is the message

Not Acceptable!
An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security.

Any thoughts or suggestions?

Thanks in advance.
Scott