This message is more than likely due to your Gmail folder settings. To fix it, open settings within Gmail (not the app), and click on the "Labels" tab. On the left hand column, you will see all of your folders/labels. Make sure the check box for "Show in IMAP" is enabled for the Gmail/All Mail folder--if it is not, please check the box to enable to it.
Back in the app, open the slide-out navigator, and then click on your email account to display all of your Gmail folders. This will sync the folder list, and you should now be able to archive mail.