Error indexing method 'QueueTrigger' Could not load type 'Azure.Core.SyncAsyncEventHandler

Question

I have an azure functions queue trigger. It's working fine locally but not when deployed. In Application Insights I could see the below error message & the queue trigger won't get invoked because of this exception. I had a .netcore 3.1 app with azure functions v3. Even I upgraded it to .net6.0 & azure functions v4. Also, I tried upgrading, downgrading & installing some packages still it didn't resolve the issue.

How to fix System.TypeLoadException - Error indexing method 'NameOfQueueTrigger'. Could not load type Azure.Core.SyncAsyncEventHandler from assembly 'Azure.Core'?

Answer 1

Microsoft removed the .NET 3.1 Support on Azure Portal Function App Deployment:

Created the .NET 3.1 Azure Function App in Local Environment (VS Code) with Queue Trigger - Tested Locally:

When deploying V3 Project to V4 Azure Portal Function App, got the below warning and deployed successfully after clicking the option “deploy anyway”:

Testing in Azure Portal:

---

I’ve migrated the Queue Trigger Function Project from .NET 3.1 to 6 and Azure Functions core tools version 3 to 4 with the below changes:

.csproj file code:

<Project  Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<!-- <TargetFramework>netcoreapp3.1</TargetFramework>
<AzureFunctionsVersion>v3</AzureFunctionsVersion> -->
<TargetFramework>net6.0</TargetFramework>
<AzureFunctionsVersion>v4</AzureFunctionsVersion>
</PropertyGroup>
<ItemGroup>
<PackageReference  Include="Microsoft.Azure.WebJobs.Extensions.Storage"  Version="4.0.5"  />
<!-- <PackageReference Include="Microsoft.NET.Sdk.Functions" Version="3.1.1" /> -->
<PackageReference  Include="Microsoft.NET.Sdk.Functions"  Version="4.1.1"  />
</ItemGroup>
<ItemGroup>
<None  Update="host.json">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
</None>
<None  Update="local.settings.json">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
<CopyToPublishDirectory>Never</CopyToPublishDirectory>
</None>
</ItemGroup>
</Project>

It asks to restore the missing dependencies after changing the versions in the .csproj file and click Restore them:

Result:

Error indexing method ‘NameOfQueueTrigger’. Could not load type Azure.Core.SyncAsyncEventHandler from assembly ‘Azure.Core’

For this error, check the following Steps:

1. Check the Connection String defined in local.settings.json and in the Function Code are same and pointing to the correct storage account and Correct Queue name:

2. Refer to the MS Q&A 503163 given by @MayankBargali-MSFT on regarding the similar issue.