can not access email on ipad but can on iphone

If you're trying to connect to a POP email account, it might be locked. Take a look at this Apple doc for more info -> iOS: 'Mailbox Locked', account is in use on another device, or prompt to re-enter POP3 password

Also, if you're connecting to your iSPs email server, you might need to be connected to the Internet over their network.

iOS: Unable to send or receive email

http://support.apple.com/kb/TS3899

Can’t Send Emails on iPad – Troubleshooting Steps

http://ipadhelp.com/ipad-help/ipad-cant-send-emails-troubleshooting-steps/

iPad Mail

http://www.apple.com/support/ipad/mail/

Try this: Delete the account in Mail and then set it up again.

 Cheers, Tom 😉