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.
- What is the Windows Phone Find My Phone functionality, and how does that work?
- How do I resize the tiles on the start screen of the Nokia Lumia to a different size?
- How can I transfer my office documents to my Nokia Lumia with Windows Phone 8?
- Which version of Windows Phone does my Lumia have?
- How do I update the phone software for my Lumia phone?