Hello @BALAKRISHNA A - Thanks for reaching out.
Usually, there is some limitation to the user for the use of resources. You get the error when you try to scale up for more nodes if the vCpu have none left. I think it's also a possible reason for you. You can take a check.
Use the az aks scale command to scale the cluster nodes using Azure CLI as described here: scale-cluster
az aks show --resource-group myResourceGroup --name myAKSCluster --query agentPoolProfiles
This will show you the descriptive error message in Azure CLI. It is likely that you exceeded the limit for the core quota.
I hope this information helps.
Please feel free to "Accept as Answer" if the above response helped, so it can be beneficial to the community.