Unable to Import Contacts

I am getting this message when trying to import contacts:

Service Unavailable

The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

Additionally, a 503 Service Unavailable error was encountered while trying to use an ErrorDocument to handle the request.

Anyone know how to get around this?

Thanks

Joelle

Does this error popup right after start importing or after some time on importing?

Regards