Description: You are unable to delete the Opportunity due to existing Estimates or Estimate Templates.
Solution: Delete any Estimates attached to the Opportunity, including any inactive Estimates – which can be viewed by checking the Show Inactive Estimates check box on the Opportunity page.
If you are unable to Delete the Opportunity despite there being no Active or Inactive Estimates, it is likely that an Estimate Template was made at some point in time from this Opportunity. If this is the case, you can Delete the Estimate Template by going to Settings and then either Construction or Maintenance Templates.
Once in the Estimate Templates page, click on the x next to the name of the Template you would like to Delete.