vs 2015-non debug ctrl-f5 works but debug mode throws and error about not being able to find localhost

Question

Hi,

I am getting this error when trying to debug in vs 2015: localhost refused to connect.

Here's the situation:

I am running vs 2015. I have been using this machine and this installation of vs2015 for 3 years. In fact both machine and vs was there before I got to my job. I was working on a c#/telerik project that I've been working on for the same 3 years. Everything has worked fine.
I changed some code (no configuration items) that used a telerik radgrid. I got to a point where I was able to go into edit mode but did not update the data entered in edit mode.
I didn't close vs or reboot or do anything except try to run in debug after the last code change I mentioned above. I got an error saying that local host could not be reached.
I tried other projects with the same application that I was working on and also tried projects with other applications and ALL OF THEM GAVE THE SAME ERROR: local host could not be reached. So this doesn't look like an issue in my project.
I uninstalled and reinstalled iis express 10 (that seems to be what is used in debug mode from what I've read). This did not fix the problem
As an experiment I ran the original project in non-debug mode (ctrl-F5) and IT DID WORK.
I've tried changing the applicationhost.config in iis express per a post I found: "change the managedruntimeversion from "v4.0" to "v4.0.30319" for .net 4.5 <add name="Clr4IntegratedAppPool" managedRuntimeVersion="v4.0.30319" managedPipelineMode="In
This is quite confusing. We did have some window updates that didn't quite work but they were attempted at least a day before this problems came up; so it seems unlikely these updates caused the error. I have gone through many posts with no success but I'll point out that none of them address the debug vs non debug mode very clearly; I don't know for sure what version of iis is used by either debug or non-debug mode . I have a feeling this is an issue with debug mode and possibly iis express but I can't be sure. Any help would be appreciated. I am considering reinstalling vs 2015 but I hope to avoid that.

Neil