When making a request to the virtual root (without a trailing slash) under IIS, the following exception is thrown:

[ArgumentOutOfRangeException: startIndex cannot be larger than length of string. Parameter name: startIndex] System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy) +10080140 System.String.Substring(Int32 startIndex) +19 mojoPortal.Web.UrlRewriter.RewriteUrl(HttpApplication app) in D:\Projects\KRB\MojoPortal\Web\Components\UrlRewriter.cs:133 mojoPortal.Web.UrlRewriter.UrlRewriter_BeginRequest(Object sender, EventArgs e) in D:\Projects\KRB\MojoPortal\Web\Components\UrlRewriter.cs:71 System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +80 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +171

That is line 133 of UrlRewriter.cs:
string targetUrl = requestPath.Substring(appRoot.Length + 1);

which can be rewriiten to fix:

string appRoot = WebUtils.GetApplicationRoot();
if (requestPath.Length == appRoot.Length)
return;
string targetUrl = requestPath.Substring(appRoot.Length + 1);

Example of url that causes exception: http://localhost/mojo (fails) as opposed to http://localhost/mojo/ (succeeds).