Data Sync Not Working with Google Mail

I have recently bought an HTC Tattoo but am having problems getting google mail to work.

I open up settings>Data Synchronisation>Google

I tick Google Mail then Menu>Sync but it doesn't sync the mail (Calendar and contacts work fine)
I have tried setting up my google mail account as an IMAP account (not sure why I would need to do this because if it is already syncing witj calendar etc then it knows this info) but this still does not work

The strange thing is I can tick the tick box next to Google Mail but when I go back into the screen the tick has gone :-(

Can anyone help??