Suspension of an account may occur when a user breaches the Rules of Conduct or User agreement. There are many reasons a user may have their account suspended. A breach of any of the aformentioned agreements can lead to a number of different actions including but not limited to: inventory clearing, character deleting, suspension, permanent banning. More information is on the official Guild Wars website.
For first time offenders, suspensions time is 72 hours. The user cannot log onto any characters, nor see friends or guild lists during this time.