How to fix the error - Could not load file or assembly 'System.Memory.Data, Version, under the Azure Durable function

Question

How to fix the error - Could not load file or assembly 'System.Memory.Data, Version, under the Azure Durable function

raviteja vemulakonda 20

I'm building a Azure Durable function with Python framework in my local VS Code. While I'm running the function in the visual studio, I'm getting the below error.

The listener for function 'Functions.orchestrator' was unable to start. Azure.Core: Could not load file or assembly 'System.Memory.Data, Version=6.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'. The system cannot find the file specified.

I'm using the Azurite for the local storage and the services are also listening under the below ports.

User's image

Hi All,

Please find the below host.json and localsettings.json

host.json

{

"version": "2.0",

"extensionBundle": {

"id": "Microsoft.Azure.Functions.ExtensionBundle",

"version": "[4.*, 5.0.0)"
```  }

}

local settings.json

{

  "IsEncrypted": false,

  "Values": {

```yaml
"AzureWebJobsStorage": "DefaultEndpointsProtocol=http;AccountName=devstoreaccount1;AccountKey=Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==;BlobEndpoint=http://127.0.0.1:10000/devstoreaccount1;QueueEndpoint=http://127.0.0.1:10001/devstoreaccount1;TableEndpoint=http://127.0.0.1:10002/devstoreaccount1;",

"FUNCTIONS_WORKER_RUNTIME": "python",

"DurableFunctionsHubName": "MyDurableFunctionsHub"
```  }

}

Could some one help me in resolving the above error.

Anonymous

2025-06-23T17:02:37.37+00:00
Hi raviteja vemulakonda,

Thanks for your query.

The error "Could not load file or assembly 'System.Memory.Data'" happens because the Azure Functions runtime is missing a required dependency.

Please try these steps to fix it:

Update Azure Functions Core Tools Use version 4.x → Install Guide

Update host.json Extension Bundle

"extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.11.0, 5.0.0)" }

Use Python 3.8, 3.9, or 3.10 only Supported Python Versions

Install .NET 6 SDK Required by the runtime → Download .NET 6

Upgrade Durable Functions Package

pip install --upgrade azure-functions-durable

After that, restart VS Code and run:

func host start

Let me know if the issue continues — happy to help further!
Anonymous

2025-06-24T14:01:54.24+00:00

Hi raviteja vemulakonda,

I hope you had a chance to review the response above. If there are any updates or if you need further assistance, please feel free to update here.
raviteja vemulakonda 20 Reputation points

2025-06-25T12:16:56.37+00:00

Hi @Anonymous ,

I have made the changes, but still getting the same error.

Please find the below configurations, that I'm using for building the durable function.

VS Code - 1.100.0

Python - 3.9

Core Tools Version - 4.0.5148

Function Runtime Version - 4.17.3.20392

.NET runtime - Microsoft.NETCore.App 6.0.16

Local Storage - Azurite
Anonymous

2025-06-26T14:32:09.9166667+00:00

Hi raviteja vemulakonda,

If you are still facing the issue, could you please check the private message and provide the required details for further troubleshooting?
Steven Nguyen 0 Reputation points

2025-06-30T14:35:56.35+00:00
Hi raviteja vemulakonda,

This issue can arise due to a few reasons. Here are some steps you can take to resolve this issue:

Ensure Dependencies are Installed

Check Python Version

Check the host.json and local.settings.json, ensure that there are no syntax errors or issues with formatting.

Kindly let me know if this works for you and whether you have further questions.

If I have answered your question, please accept this as answer and give a thumbs up for "Was it helpful"!

Best regards,

Steven Nguyen

Answer accepted by question author

1 additional answer

Your answer

Anonymous

2025-06-23T17:02:37.37+00:00

Hi raviteja vemulakonda,

Thanks for your query.

The error "Could not load file or assembly 'System.Memory.Data'" happens because the Azure Functions runtime is missing a required dependency.

Please try these steps to fix it:

Update Azure Functions Core Tools Use version 4.x → Install Guide

Update host.json Extension Bundle

"extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.11.0, 5.0.0)" }

Use Python 3.8, 3.9, or 3.10 only Supported Python Versions

Install .NET 6 SDK Required by the runtime → Download .NET 6

Upgrade Durable Functions Package

pip install --upgrade azure-functions-durable

After that, restart VS Code and run:

func host start

Let me know if the issue continues — happy to help further!
Anonymous

2025-06-24T14:01:54.24+00:00

Hi raviteja vemulakonda,

I hope you had a chance to review the response above. If there are any updates or if you need further assistance, please feel free to update here.
raviteja vemulakonda 20 Reputation points

2025-06-25T12:16:56.37+00:00

Hi @Anonymous ,

I have made the changes, but still getting the same error.

Please find the below configurations, that I'm using for building the durable function.

VS Code - 1.100.0

Python - 3.9

Core Tools Version - 4.0.5148

Function Runtime Version - 4.17.3.20392

.NET runtime - Microsoft.NETCore.App 6.0.16

Local Storage - Azurite
Anonymous

2025-06-26T14:32:09.9166667+00:00

Hi raviteja vemulakonda,

If you are still facing the issue, could you please check the private message and provide the required details for further troubleshooting?
Steven Nguyen 0 Reputation points

2025-06-30T14:35:56.35+00:00

Hi raviteja vemulakonda,

This issue can arise due to a few reasons. Here are some steps you can take to resolve this issue:

Ensure Dependencies are Installed

Check Python Version

Check the host.json and local.settings.json, ensure that there are no syntax errors or issues with formatting.

Kindly let me know if this works for you and whether you have further questions.

If I have answered your question, please accept this as answer and give a thumbs up for "Was it helpful"!

Best regards,

Steven Nguyen

Answer 1

Hello raviteja vemulakonda,

Thanks for your patience on this. I am summarizing our offline discussion and posting the same as answer for the benefit of other community members.

Issue : You are encountering the following error with the Azure Durable Function: "Could not load file or assembly 'System.Memory.Data, Version'."

Mitigation/Workaround:

Updated your host.json to the following: { "version": "2.0", "extensionBundle": {
```
"id": "Microsoft.Azure.Functions.ExtensionBundle",

"version": "[3.3.0, 4.0.0)"
```
} }
Extension Bundle 3 is the final version that provides exclusive support for Python without requiring .NET dependencies. Versions 4 and above are intended for .NET-isolated workers and may lead to unexpected assembly loading errors.

Please do let us know in case of further queries, I would be happy to assist you.

Please 'Accept as answer' and ‘Upvote’ if it helped so that it can help others in the community looking for help on similar topics.
User's image Thankyou!

Answer 2

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How to fix the error - Could not load file or assembly 'System.Memory.Data, Version, under the Azure Durable function

1 additional answer

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