One thing that has annoyed me for a long time is that on my machines, at least, with Windows 10, if you double-click on a .ossln file in Windows Explorer, it tries to reload some part of Visual Studio 2015. It is way past annoying. Well, I think I have fixed it. I haven't rebooted so I am not 100% confident, but I wanted to cut and paste the solution before I did. I guess I can delete it if it doesn't work permanently...

First of all, the Windows Settings Set Default Programs doesn't help. You have to use a command line. The first command you could do is "assoc" all by itself. That will return a list of all associations between extensions and some sort of file designator. There you will see that there is an association between .ossln. It is:

C:\Users\edward.lebeau>assoc
.ossln=OpenSpan.OpenSpan Studio for Microsoft Visual Studio 2015.ossln

The other command to use is "ftype". If you just enter ftype, you will get a list program identifiers and the command line entries that Windows should make to execute that program identifier. So "assoc" creates an identifier for the extension. ftype provides the execution information for the identifier.

I did an ftype command for the above identifier, and it was not found. And that's the problem.

C:\Users\edward.lebeau>ftype OpenSpan.OpenSpan Studio for Microsoft Visual Studio 2015.ossln
File type 'OpenSpan.OpenSpan Studio for Microsoft Visual Studio' not found or no open command associated with it.

But rather than mess with that yucky identifier, I decided to replace it with a simple "OpenSpan". So here are the two entries to make it work:

C:\Windows\System32>assoc .ossln=OpenSpan
.ossln=OpenSpan

C:\Windows\System32>ftype OpenSpan="C:\Program Files (x86)\OpenSpan\OpenSpan Studio for Microsoft Visual Studio 2015\OpenSpan.Studio.Shell.exe" "%1"
OpenSpan="C:\Program Files (x86)\OpenSpan\OpenSpan Studio for Microsoft Visual Studio 2015\OpenSpan.Studio.Shell.exe" "%1"

Maybe with this information, Pega can fix the problem permanently. In the meantime, I can click on the .ossln from a history list and it will open for me...l