I installed from:
https://github.com/npgsql/npgsql/releases/download/v3.2.6/Npgsql-3.2.6.msi
I checked the GAC:
** Visual Studio 2017 Developer Command Prompt v15.6.4
** Copyright (c) 2017 Microsoft Corporation
C:\Windows\System32>gacutil /l npgsql
Microsoft (R) .NET Global Assembly Cache Utility. Version 4.0.30319.0
Copyright (c) Microsoft Corporation. All rights reserved.
The Global Assembly Cache contains the following assemblies:
npgsql, Version=3.2.6.0, Culture=neutral, PublicKeyToken=5d8b90d52f46fda7, processorArchitecture=MSIL
Number of items = 1
And double checked C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config
<system.data>
<DbProviderFactories>
<add name="Npgsql Data Provider" invariant="Npgsql" description=".Net Data Provider for PostgreSQL" type="Npgsql.NpgsqlFactory, Npgsql, Culture=neutral, PublicKeyToken=5d8b90d52f46fda7"/>
</DbProviderFactories>
</system.data>
A little more about my environment:
When I first upgraded llblgen, I was running both 3.5 and 5.3 so that I could start a new project with the new features of 5.3. Now, I just got a new laptop, and I would like to leave v3.5 behind and only run 5.3 on the new laptop (which means convert the old one).
I still have my old laptop here, waiting to be wiped, but this is the one issue that I need to resolve before I can (I'm still dependent on 3.5 until I can get my project converted).
I figured it was worth checking to see what happens when I create a database-first project from scratch, and I still get the same error when I select the PostgreSql Driver (npgsql) item from the Database Driver dropdown.
... Looking into this further:
On my old laptop, I noticed that I did not have npgsql installed in the GAC. I just installed it. The same install as the new laptop, and I was able to get past that exception. That's a good sign!
Now, on the new laptop, I just uninstalled and reinstalled npgsql; I confirmed that it was removed and then added back into the GAC. I still get the exception.
I've reached out to my infrastructure team. They install a nasty blend of AntiVirus software and have some pretty tight security policies on these laptops. Hopefully, they will get back with me soon and I'll have some luck, but in the meantime, I wanted to share my status.