Sites of WP MultiSite Stopped Working.

Hi,

For some unknown reason, our sites stopped working...nothing on WP was changed.

The main site i.e http://topsiteblog.info/ works and we are able to login as admin to the backend.

Example of sites that dont work are:
http://grand-canyon.topsiteblog.info/
http://porsche.topsiteblog.info/
http://hellokitty.topsiteblog.info/

Would this be anything related to sub-domain ? or.. ?

Awaiting some feedback and/or thoughts...

Thanks & Regards