Symptoms

Unable to edit workflows in K2 Designer with error "External component has thrown an exception"
 

Diagnoses

We checked the windows application logs and found an error message thrown at the same time which stated:

Event code: 3007
Event message: A compilation error has occurred.

Faulting application name: vbc.exe, version: 14.0.81.0, time stamp: 0x5584f0f2
Faulting module name: sSYSTEM32MSVCP120_CLR0400.dll!__crtGetFileInformationByHandle, version: 6.3.9600.18007, time stamp: 0x55c4c16b
...

Based on this information, we found a Microsoft KB article:

https://support.microsoft.com/en-us/kb/3118750
 

Resolution

In this case, .NET 4.6 was not installed on the server which we verified via the registry. We found only .NET versions up to 4.x. Visual studio 2015 was installed on another machine (not the server), so this case did not seem to exactly match the scenario outlined in the Microsoft KB article, however, we removed the MS updates 3098779 and 3097997 and the issue was resolved.