clr-activation-debugging

SKILL.md

CLR Activation Debugging

Diagnose .NET Framework runtime activation issues by analyzing CLR activation logs (CLRLoad logs) produced by the shim (mscoree.dll). These logs record every decision the shim makes when selecting and loading a CLR version.

When to Use

A process fails to load the CLR at all ("Unable to find a version of the runtime to use")

The shim picks the wrong CLR version (e.g., v2.0 instead of v4.0)

Unexpected .NET 3.5 Feature-on-Demand (FOD) install dialogs appear

FOD dialogs are expected but do NOT appear

Both CLR v2 and CLR v4 load into the same process, causing failures

A COM object fails to activate because the shim can't resolve the runtime

Legacy hosting APIs (CorBindToRuntime) bind to an unexpected version

When Not to Use

Modern .NET (CoreCLR / .NET 5+) — this skill covers .NET Framework only (the mscoree.dll shim)

Assembly binding failures — use Fusion logs (fuslogvw.exe), not CLR activation logs

Runtime crashes after the CLR has loaded — activation succeeded; the problem is elsewhere