Ranjit Singh, are you still facing this issue? Can you please answer the following to help gain more details of the issue
- share the error details/screenshot for the error you are getting.
- Are you facing this issue only with a particular resource group? What happens if you create a new resource group and then try to delete it?
- It might be possible that the RG contains a resource (which could be hidden) on which there is a dependency from other resource (probably in another resource group). Check the Hidden Resource Types in the portal as shown below to get all the hidden resources in this resource group
For this issue, I would suggest looking in the activity logs to check the cause of this issue. To access it, search for "Monitor" in Azure Portal and click "Activity Log". Ensure to select the TimeSpan (around time when you tried to delete the RG) and filter properly to see all events.
Please let us know if you have any questions.