Chances are it's the actual text of the password or user name that is causing the problem, but fiing it is easy and also pervents your users accidentally or deliberately destroying your database - use parametrised queries:
dbCom.CommandText = "UPDATE loginDB SET password=@PW WHERE ID=@ID";
dbCom.Connection = dbCon;
But please, never store passwords in clear text - it is a major security risk. There is some information on how to do it here: Password Storage: How to do it.