Hi Boizan.
Thank you for supplying the name of your product.
I checked our product knowledgebase at
http://www.support.xerox.com/support/workcentre-6015/support/enus.html
I found a recommended solution for Fault Code 031-555: SMB Error. Scan login Failed Message.
http://www.support.xerox.com/support/WC6015/support/en_US.html?objGUID=20921
Clink on this link to follow the recommended steps.
Power Off the Printer, Wait 10 Seconds, and then power on the printer.
Please try and see if this helps.