Should have said I am registering it like so

UrlProviderResolver.Current.InsertTypeBefore<DefaultUrlProvider, ServiceUrlProvider>();

Can you post the code for the UrlProvider? The issue appears to be there I think.

I have just changed it and still get the same error. I have this in application starting.

        UrlProviderResolver.Current.InsertType<ServiceUrlProvider>();

And this is my ServiceUrlProvider

public class ServiceUrlProvider : DefaultUrlProvider
{
    public override string GetUrl(UmbracoContext umbracoContext, int id, Uri current, UrlProviderMode mode)
    {
        var content = umbracoContext.ContentCache.GetById(id);
        if (content.DocumentTypeAlias == "Service" && content.Parent != null)
        {
            // Get the last part of the url
            var currentUrl = content.Url;
            var splitSections = currentUrl.Split(new[] { '/' }, StringSplitOptions.RemoveEmptyEntries);
            return string.Concat("/",splitSections.Last(), "/");
        }
        return base.GetUrl(umbracoContext, id, current, mode);
    }
}

But I just keep getting the StackOverFlow exception... ?

Well this is awkward lol. Thanks Carl. I thought I had changed that to

base.GetUrl(umbracoContext, id, current, mode);

But too blindly changing things!! Thanks.

I think that Carl is correct, I would replace it with

var currentUrl=base.GetUrl(umbracoContext, id, current, mode);

is working on a reply...