System.TypeInitializationException

A TypeInitializationException is thrown when a static constructor or a static field initializer throws. The runtime wraps the original exception in this one, and the message only says The type initializer for 'X' threw an exception.

The type is never usable after that. Every later access to the class throws the same exception, so one failed initializer can show up many times in a log, long after the first failure.

Statistics

16

34

Common causes

The wrapper is never the problem. The original exception is in InnerException, and the stack trace has the line of the initializer. Typical causes:

public static class ExchangeRates
{
    public static readonly Dictionary<string, decimal> Rates = Load();

    static Dictionary<string, decimal> Load()
    {
        var json = File.ReadAllText("rates.json");
        return new Dictionary<string, decimal>();
    }
}

public static class ExchangeRates
{
    private static Dictionary<string, decimal> _rates;

    public static Dictionary<string, decimal> GetRates()
    {
        return _rates ??= Load();
    }

    static Dictionary<string, decimal> Load()
    {
        var json = File.ReadAllText(Path.Combine(AppContext.BaseDirectory, "rates.json"));
        return new Dictionary<string, decimal>();
    }
}

public static class Endpoints
{
    public static readonly Uri Prices = new Uri(Environment.GetEnvironmentVariable("PRICES_URL"));
}

public class EndpointOptions
{
    public string PricesUrl { get; set; }
}

public class EndpointValidator
{
    public Uri GetPricesUri(EndpointOptions options)
    {
        if (string.IsNullOrEmpty(options.PricesUrl))
            throw new InvalidOperationException("PricesUrl is not configured.");

        return new Uri(options.PricesUrl);
    }
}

public static class Defaults
{
    public static readonly string Currency = Prefix.ToUpper();   // Prefix is still null here
    public static readonly string Prefix = "dkk";
}

public static class Defaults
{
    public static readonly string Prefix = "dkk";
    public static readonly string Currency = Prefix.ToUpper();
}

How to fix it and prevent it

static class Rates
{
    public static readonly int Count = int.Parse("x");
}

public void Show()
{
    try
    {
        _ = Rates.Count;
    }
    catch (TypeInitializationException e)
    {
        Console.WriteLine($"{e.TypeName} failed: {e.InnerException?.Message}");
    }
}

How to read the stack trace

The outer exception is the wrapper, and the real error comes after --->:

System.TypeInitializationException: The type initializer for 'Shop.Services.ExchangeRates' threw an exception.
 ---> System.IO.FileNotFoundException: Could not find file 'C:\src\Shop\bin\Debug\net10.0\rates.json'.
File name: 'C:\src\Shop\bin\Debug\net10.0\rates.json'
   at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options)
   at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.Strategies.OSFileStreamStrategy..ctor(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.Strategies.FileStreamHelpers.ChooseStrategyCore(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
   at System.IO.StreamReader.ValidateArgsAndOpenPath(String path, Int32 bufferSize)
   at System.IO.File.ReadAllText(String path, Encoding encoding)
   at Shop.Services.ExchangeRates.Load() in C:\src\Shop\Services\ExchangeRates.cs:line 7
   at Shop.Services.ExchangeRates..cctor() in C:\src\Shop\Services\ExchangeRates.cs:line 4
   --- End of inner exception stack trace ---
   at Program.<Main>$(String[] args) in C:\src\Shop\Program.cs:line 4

The inner exception is a FileNotFoundException for rates.json. The frames show that ExchangeRates.Load on line 7 was called from the static constructor, ..cctor, on line 4. The line at the bottom, Program.cs line 4, is only the first code that used the class. Fix the file problem, and the type loads.

Should you catch it?

Catching it does not bring the type back, since every use of the class throws again. Catch it at the place where you can log the inner exception and show an error.

Because later uses repeat the same exception, find the first one in the log. It has the stack trace of the real error.

Related exceptions

• FileNotFoundException is a common inner exception, when a static initializer reads a file.
• TypeLoadException is thrown when a type cannot be loaded at all.
• NullReferenceException is another common inner exception, from fields that are used before they are set.

Frequently asked questions

Let your AI agent track it down

Connect Claude Code, Cursor, VS Code or Visual Studio to the elmah.io MCP server and ask your agent to look into TypeInitializationException for you. For example:

The agent reads the stack trace and request details from elmah.io, finds the code in your repository and proposes a fix. In Claude Code, add the server with one command:

claude mcp add --transport http --client-id claudecode elmahio https://mcp.elmah.io/mcp

The MCP server is included on every plan and is currently in beta. Set up the MCP server.

Further reading

YouTube videos

Answers from Stack Overflow

<dependentAssembly>
  <assemblyIdentity name="System.Threading.Tasks.Extensions" publicKeyToken="cc7b13ffcd2ddd51" culture="neutral" />
  <bindingRedirect oldVersion="0.0.0.0-4.2.0.1" newVersion="4.2.0.1" />
</dependentAssembly>

Update-Package -reinstall -Project <your project name>

Source: Stack Overflow