The mailbox may have some emails with an excessively long subject line that are not supported by Windows Phone 8. Once you have removed the suspect mail item (i.e. cleaned the mailbox or move the suspect mail to a folder that phone does not sync) the error will cease.
- When will Lumia Black update be available?
- What content can I copy using Transfer my Data app from an old phone to my new Nokia Lumia?
- Emails sent with my Lumia do not appear in Yahoo! Mail
- How can I transfer my phone data onto my new Lumia phone?
- How can I get the Transfer my Data application on my Nokia Lumia with Windows Phone 8?