There is a limitation 1 managed package can be created in developer edition. I created one managed package, but then deleted it. Now I am trying to create another one but I get error: "You are only allowed one managed package per salesforce.com instance". Is there any room I could TOTALLY remove old managed package? I don't see it, thus I can not remove or update it. Thank you.
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2You will need to contact support. If it can be done, they can do it. If not, you'll have to create a new developer org. – sfdcfox May 12 '16 at 15:34
Given that Developer Editions are free your best option is to create a new one and then create the new Managed Package in that, DE Orgs are not really a priority for Salesforce support so even if you contact them it may take time to get resolved.