Help me with this error message: Validation failed. Required information is missing or invalid.

Question

My users could not connect because I did not have enough VMs. I went through the steps of adding more VMs. When the system tries to validate this increase in VMs, it fails with the above error message. I need to know how to fix it.

Answer 1

Hello @Kevin Yoo,

Thanks for using Q and A forum.

When you encounter an error while trying to increase the number of virtual machines (VMs) in Azure, it may be due to insufficient IP addresses available in the pool for the new VMs. To resolve this issue, you should verify that there are enough IP addresses left in the pool to create additional VMs.

PowerShell

(Get-VM | Get-VMNetworkAdapter).IPAddresses | fl

This will help you confirm whether the IP addresses have been properly assigned and if there are any available for new VMs. If the pool is exhausted, need to adjust your network settings to free up or allocate more IP addresses

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Answer 2

Hello @Kevin Yoo

Thank you for contacting us about the VM issue.

This validation error occurs when Azure Virtual Desktop detects missing or inconsistent prerequisites while adding new session host VMs. The message is generic, but in practice it is caused by configuration or capacity issues.

Step1. Validate subnet capacity :

1. Go to Azure Portal → Virtual Network
2. Open the subnet used by the session hosts
3. Confirm that at least 1 free IP per new VM is available
   • If IPs are < required count:
   • Expand the subnet range or
   • Use a new subnet

Step2. Re‑confirm VM size availability in the region :

1. Go to Subscriptions → Usage + quotas
2. Check:
   • VM family quota for the selected region
   • VM SKU availability
3. If the SKU is constrained:
   • Select a different VM size
   • Retry the scaling operation

Step3. Revalidate host pool configuration

1. Open Azure Virtual Desktop → Host pools
2. Check:
   • Assignment type (Pooled / Personal)
   • Domain join settings (AD / Azure AD)
   • Image source (Marketplace / Shared Image Gallery)
3. Ensure new VMs match existing session hosts

Step4. Confirm permissions :

Ensure the user or automation account has Contributor or higher permissions on:

• Host pool resource
• Session host VMs resource group
• Virtual Network
• Image / Gallery

After adjusting permissions: Sign out → Sign back in → Retry the operation.

Step5. Clean up failed session hosts :
If earlier scale‑out attempts partially failed:

1. Go to Host pool → Session hosts
2. Remove:
   • Failed.
   • Unavailable.
   • Disconnected hosts that never fully provisioned.
3. Retry adding VMs

This step has resolved validation failures in cases where backend state was blocked.

The error is typically caused by subnet IP exhaustion, VM SKU constraints, permission gaps, or configuration mismatches. Once these were corrected, the validation passed and VM scaling completed successfully in similar Azure Virtual Desktop deployments.

Links :
https://learn.microsoft.com/en-us/azure/virtual-network/ip-services/
https://learn.microsoft.com/en-us/azure/role-based-access-control/overview

Thanks,
Manish Deshpande.

Answer 3

I have checked these things and they do not seem to be the problem.