Mendeley are in the process of transitioning their log ins to a different server, which means that access via the usual web address: http://www.mendeley.com can be unreliable. If you try to log in via this address and receive a message: “We’re sorry but we can’t sign you in at the moment. Please try again later”, please log in via: https://mendeley.com/sign/in/plus instead. Once the transition process has been completed the usual Mendeley address will be working again. Mendeley apologise for the inconvenience.