Custom table in Uniselector in Kentico

I have been using Kentico without issue for a while until today, here is my issue

I want to use Custom table in uniselector.

How I came into the issue was, I need to use Custom Form Controls, like in SiteManager->Users Advanced filter. We have Add Roles which opens a popup and it shows list of all roles.

This webpart uses Uniselector

<cms:CMSUpdatePanel ID="pnlUpdate" runat="server">
<ContentTemplate>
    <cms:UniSelector ObjectType="cms.role" SelectionMode="MultipleTextBox"
        OrderBy="RoleDisplayName" ResourcePrefix="roleselect" runat="server"
        ID="usRoles" ShortID="s" AllowEditTextBox="true" AddGlobalObjectSuffix="true" />
</ContentTemplate>
</cms:CMSUpdatePanel>

Now if I use

ObjectType="cms.role" 

it works fine because it is system table

now if I use.

ObjectType="customtable.country"

This will not work

Any help is appreciated. Thanks in advance.