NavMenu.razor(1,5): error RZ10007: The attribute 'class' is used two or more times for this element. Attributes must be unique (case-insensitive)

[Evangelink]

Build Information

Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1468444
Build error leg or test failing: Microsoft.NET.Sdk.Razor.Tests.BuildWithComponents31IntegrationTest.Build_Components_WithDotNetCoreMSBuild_Works
Pull request: #54725

Details

Exception Message

Expected value to be 0 because Expected command to pass but it did not.
Working Directory:
File Name: /tmp/helix/working/B15F0905/p/d/dotnet
Arguments: msbuild /t:Build /private/tmp/helix/working/B15F0905/t/dotnetSdkTests.TCij1Hxk/Build_Compone---DE8ABFA8/blazor31.csproj /restore
Exit Code: 1
StdOut:
MSBuild version 18.9.0-preview-26311-113+50e862b8d for .NET
  Determining projects to restore...
  Restored /private/tmp/helix/working/B15F0905/t/dotnetSdkTests.TCij1Hxk/Build_Compone---DE8ABFA8/blazor31.csproj (in 2.24 sec).
/tmp/helix/working/B15F0905/p/d/sdk/11.0.100-ci/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.RuntimeIdentifierInference.targets(385,5): message NETSDK1057: You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy [/private/tmp/helix/working/B15F0905/t/dotnetSdkTests.TCij1Hxk/Build_Compone---DE8ABFA8/blazor31.csproj]
/private/tmp/helix/working/B15F0905/t/dotnetSdkTests.TCij1Hxk/Build_Compone---DE8ABFA8/Shared/NavMenu.razor(1,5): error RZ10007: The attribute 'class' is used two or more times for this element. Attributes must be unique (case-insensitive). [/private/tmp/helix/working/B15F0905/t/dotnetSdkTests.TCij1Hxk/Build_Compone---DE8ABFA8/blazor31.csproj]
StdErr:
, but found 1 (difference of 1).

CallStack

at FluentAssertions.Execution.LateBoundTestFramework.Throw(String message)
   at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
   at FluentAssertions.Execution.AssertionScope.AddPreFormattedFailure(String formattedFailureMessage)
   at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
   at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
   at FluentAssertions.Execution.AssertionChain.FailWith(String message, Object[] args)
   at FluentAssertions.Numeric.NumericAssertionsBase`3.Be(T expected, String because, Object[] becauseArgs)
   at Microsoft.NET.TestFramework.Assertions.CommandResultAssertions.Pass() in /_/test/Microsoft.NET.TestFramework/Assertions/CommandResultAssertions.cs:line 27
   at Microsoft.NET.Sdk.Razor.Tests.BuildWithComponents31IntegrationTest.Build_Components_WithDotNetCoreMSBuild_Works() in /_/test/Microsoft.NET.Sdk.Razor.Tests/BuildWithComponents31IntegrationTest.cs:line 17
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

Error Message

DO NOT USE JSON BELOW IF THIS IS A BUILD BREAK otherwise build analysis will allow pull requests to merge that break the build worse. For a build break, do not use this issue form. Make a regular new issue.

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "NavMenu.razor(1,5): error RZ10007: The attribute 'class' is used two or more times for this element. Attributes must be unique (case-insensitive)",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1468444
Error message validated: [NavMenu.razor(1,5): error RZ10007: The attribute 'class' is used two or more times for this element. Attributes must be unique (case-insensitive)]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 6/17/2026 3:23:18 PM UTC

Report

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	0	0

[github-actions]

This Known Build Error has had 0 hits in the past month and has been labeled stale. It will be auto-closed in 7 days if the hit count remains at 0. Add the keep-open label to prevent auto-closure.

[github-actions]

Closed automatically — this Known Build Error has had 0 hits for over a month.