.net Tableadapter to string

Question

i get the error "DataSetSharedkey.sharedkeyDBDataTable can not converted to string

    Dim sharedkeyFromDB As New DataSetSharedKeyTableAdapters.sharedkeyDBTableAdapter
    Dim test As String = sharedkeyFromDB.GetSharedkeyByUsername(tbUserName.ToString)

my GetSharedkeyByUsername Statment look like

SELECT sharedKey FROM sharedkeyDB WHERE (UserName = @UserName)