Everytime I check my mail this comes up? Description below

Everytime I check my mail this box pops up and the only option is ok so I can't get any mail or send any on my gmail account on my iPhone! It says
Can't Get Mail
The mail server "imap.gmail.com" is not responding. Verify that you have entered the correct account info in mail settings.
Ok
Help! What does this mean and how can I get rid off it to check my mail x thanks.

The message states that the server is down so there really isn't anything that you can do except wait until Google fixes things at its end.

For some reason, GMail isn't sending mail details to your phone. There are heaps of reasons this is happening, the easiest way to sort this is to delete/remove the account and re-add it making sure you get the P/W and address OK.

EDIT

It's very unlikely that the server is down, imap.gmail is a cluster and resources will failover to another server if the one you're connected to goes down. It looks very much like your iPhone is not providing the correct credentials, iPhones tend to act like it's never their fault, hence the slightly misleading message…