This is one of those reminder’s to myself…

Don’t forget that you can use fuslogvw to find problems loading assemblies.

Why do I need reminding?

I had an issue whereby a release build of an application I was working on had been configured for live/prod for the first time and somebody went to test the application which simply failed at start-up – just displaying a Windows dialog asking whether I wanted to close or debug the application.

Ofcourse, the application worked perfectly on my machine and oddly the non-prod versions also worked fine on the other user’s machine. However the live/prod release had one change to the previous build. A new feature had been removed which wasn’t ready to go live and unbeknown to me, the removal of it’s project caused the build to deploy older versions of a couple of DLL’s as part of the new live/prod build.

On my machine this wasn’t an issue as .NET located the newer versions of the DLL’s, on the other user’s machines these could not be located.

This is fine, it was all part of pre-release testing cycle but a little confusing as all the non-prod configurations worked fine on other user’s machines.

When do we get to fuslogvw?

I haven’t had the need to use fuslogvw for ages, but really should probably use it a lot more. To be honest, it makes sense to have it on all the time to catch such potential issues.

What fuslogvw can do is list any failures during start-up of a .NET application. Running fuxlogvw.exe from the Windows SDK folder (for example C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.7.1 Tools) will result in the fuslog UI being displayed. As you might have guessed from the name the fus-log-vw is a viewer for the fusion log files.

Note: You must run fuslogvw as Admin if you want to change the settings, i.e. set the path of the log files, change the level of loggin, i.e. I just wanted to log all the bind failures, etc.

Leave fuslogvw open and then run the .NET application you’re wanting to take a look at. Now you’ll need to press the Refresh button on fuslogvw to see the logs after the application has started and depending on what you are logging you may see either a list of assemblies that were loaded (for example when just logging everything) or see failures etc.

We can now see what assembly and what version of that assembly the application (we’re monitoring) tried to load and we can inspect the log itself for more information on the failure (via the log file or the fuslogvw).

It’s as simple as that.