Troubleshooting Blazor Application Issues Print

Common Blazor Deployment Issues

HTTP 500.19 - Internal Server Error

Cause: Invalid web.config or missing URL Rewrite Module

Solutions:

• Verify web.config syntax is valid XML
• Contact support to confirm URL Rewrite Module is installed
• Check file permissions on the publish folder

Blank Page / App Doesnt Load

Causes:

• Missing static files
• Incorrect base path
• JavaScript errors

Solutions:

1. Open browser Developer Tools (F12)
2. Check Console tab for errors
3. Check Network tab for failed requests (404s)
4. Verify all files from wwwroot were uploaded
5. Check <base href="/"> in index.html matches your setup

"Failed to find a valid digest" Error

Cause: Integrity check failure for Blazor WebAssembly files

Solutions:

• Re-publish and re-upload all files
• Clear browser cache
• Ensure files werent modified during upload
• Use binary mode for FTP transfers

.wasm Files Return 404

Cause: MIME type not configured for WebAssembly files

Solution: Add to web.config:

<staticContent>
  <mimeMap fileExtension=".wasm" mimeType="application/wasm" />
</staticContent>

.dll Files Return 404

Cause: IIS blocks .dll files by default

Solution: Add to web.config:

<staticContent>
  <mimeMap fileExtension=".dll" mimeType="application/octet-stream" />
</staticContent>

Blazor Server Issues

"Circuit disconnected" / Connection Lost

Causes:

• Network instability
• Server timeout
• SignalR configuration issues

Solutions:

• Check network connectivity
• Increase SignalR timeout in configuration
• Implement reconnection logic

SignalR Connection Fails

Causes:

• WebSocket not enabled
• Firewall blocking WebSocket
• Proxy interference

Solutions:

• Contact support to verify WebSocket is enabled
• Check if using CloudFlare or similar proxy
• Consider Long Polling fallback

Blazor WebAssembly Issues

Slow Initial Load

Causes:

• Large download size
• No compression
• No caching

Solutions:

• Enable Brotli/Gzip compression
• Use lazy loading for assemblies
• Implement caching headers
• Consider AOT compilation (increases size but improves runtime)

"Out of Memory" in Browser

Cause: Application using too much memory

Solutions:

• Implement proper disposal of resources
• Use virtualization for large lists
• Optimize component lifecycle

General Debugging Tips

Enable Detailed Errors

In Program.cs (Development only):

if (app.Environment.IsDevelopment())
{
    app.UseDeveloperExceptionPage();
}

Enable Blazor Debugging

In launchSettings.json:

"inspectUri": "{wsProtocol}://{url.hostname}:{url.port}/_framework/debug/ws-proxy?browser={browserInspectUri}"

Check Browser Console

1. Press F12 to open Developer Tools
2. Go to Console tab
3. Look for JavaScript errors or exceptions
4. Check for failed network requests in Network tab

Enable Logging

In appsettings.json:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning",
      "Microsoft.AspNetCore.Components": "Debug"
    }
  }
}

Getting Help

If issues persist, contact support with:

• Domain name
• Exact error message
• Browser console output
• Steps to reproduce