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.
- How can I check the IMEI number of my Lumia phone?
- What can I do if the latest Lumia extras are missing on my phone?
- What Bluetooth profiles are used on my Lumia phone?
- Why are the photos taken by Lumia Selfie different than with a normal camera on my phone?
- NFC pairing of the Wireless Charging Plate (DT-903) is not working Device Hub, what can I do?