After the restart, return to the same menu, the boxes, and let Windows download the files again. 3. Run System File Checker (SFC) and DISM
The following solutions are ordered from least invasive (safe, quick) to most invasive (system-level changes).
The error message "A fatal error has occurred loading the metadata for mscorlib.dll" After the restart, return to the same menu,
Compile manually:
Uncheck the boxes for (both 3.5 and 4.8 or later), click OK , and restart. The error message "A fatal error has occurred
Or, as a simpler alternative, delete the contents of: C:\Windows\Microsoft.NET\NativeImages_v4.0.30319\ (back up first).
The error "A fatal error has occurred loading the metadata for mscorlib.dll" is rarely a false alarm. In 90% of cases, the solutions above—clearing NGEN cache, running DISM/SFC, repairing .NET, or replacing the DLL from a healthy source—will restore functionality. In 90% of cases, the solutions above—clearing NGEN
Download from Microsoft, run it, and follow the prompts. It can detect and fix metadata corruption automatically.
The error typically occurs when the .NET Framework is corrupted, or when a development environment (like Visual Studio) cannot correctly reference this core library . mscorlib.dll (Microsoft Common Object Runtime Library) is critical because it contains the basic classes and methods (e.g., System.Object , System.DateTime ) that all .NET applications require to run. Common Causes