ado.net one to many relation

Im running into a problem using ado.net when I am trying to make a relationship between two tables i get an error that says either I am having a problem with constraints or there is Child records that dont have a parent which is not the case. I have no problem creating a relationship between tables that are one to one just one (parent) to many(child) There are multiple fields that are set to be the primary key on the child table could this be a prob. Most of this ado.net and .net stuff Ive been learning has been fairly easy just hit a wall on this issue.