Encoded character is used instead the correct one

<iframe scrolling="yes" runat="server" title="Par Selection" id="iFrame"
    frameborder="0" enableviewstate="true" width="100%" height="490" />

iFrame.Attributes.Add("src", String.Format(
            "https://www.parurval.se/urval/?username={0}&password={1}",
            parSettings.GetSettings(parSettings.SettingsType.PARSelection, parSettings.SectionType.Username),
            parSettings.GetSettings(parSettings.SettingsType.PARSelection, parSettings.SectionType.Password)));

<iframe id="tcMain_tabPARSelection_iFrame" scrolling="yes" title="Par Selection"
   frameborder="0" width="100%" height="490"
   src="https://www.parurval.se/urval/?username=myUsername&password=myPassword">
</iframe>

... src="https://www.parurval.se/urval/" ...

HttpUtility.HtmlEncode(String.Format("https://www.parurval.se/urval/?username={0}&password={1}",
parSettings.GetSettings(parSettings.SettingsType.PARSelection, parSettings.SectionType.Username),
parSettings.GetSettings(parSettings.SettingsType.PARSelection, parSettings.SectionType.Password)));