Umbraco CMS - startindex cannot be less than zero error is showing instead of 404 error page

Question

I am running into an issue with an Umbraco website.
If I miskey the URL on a top level page, e.g. mysite.com/wrongpage I get an asp error.
If I miskey it on a subpage, even if the top level page is incorrect too, I get my correct 404 error e.g. mysite.com/wrongpage/wrongpage2
At this point I'm trying to find out whether it's a bug in Umbraco 4.11.10 or if this error is caused by something obvious. I'm completely stuck and not particularly technical (I'm not a developer).
If anyone could help explain what this error means, and/or if there's any way to correct or bypass it I would really appreciate the help.
The full contents of the error are: 
Server Error in '/' Application.
StartIndex cannot be less than zero.
Parameter name: startIndex
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.ArgumentOutOfRangeException: StartIndex cannot be less than zero.
Parameter name: startIndex
Source Error: 
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace: 
[ArgumentOutOfRangeException: StartIndex cannot be less than zero.
Parameter name: startIndex]
System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy) [phone]
System.String.Substring(Int32 startIndex) +12
AutoFolders.NotFoundHandler.Execute(String url) +538
Umbraco.Web.Routing.LookupByNotFoundHandlers.HandlePageNotFound(PublishedContentRequest docRequest) +1148
Umbraco.Web.Routing.LookupByNotFoundHandlers.TrySetDocument(PublishedContentRequest docRequest) +10
Umbraco.Web.Routing.PublishedContentRequestBuilder.<LookupDocument1>b__1e(IPublishedContentLookup lookup) +15
System.Linq.Enumerable.Any(IEnumerable`1 source, Func`2 predicate) +146
Umbraco.Web.Routing.PublishedContentRequestBuilder.LookupDocument1() +198
Umbraco.Web.Routing.PublishedContentRequestBuilder.LookupDocument() +195
Umbraco.Web.Routing.PublishedContentRequest.ProcessRequest(HttpContextBase httpContext, UmbracoContext umbracoContext, Action`1 onSuccess) +139
Umbraco.Web.UmbracoModule.ProcessRequest(HttpContextBase httpContext) +339
Umbraco.Web.UmbracoModule.<Init>b__7(Object sender, EventArgs e) +80
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +136
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69

Answer 1

Hi Aaronb9,
Since the issue regards ASP.NET and website deployment. I suggestion you post the question in the ASP.NET forums at
http://forums.asp.net/. It is appropriate and more experts will assist you.
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