Error when trying to purchase reserved instance

I get the following error when trying to purchase a reserved instance. Error: Your current quota does not allow you to purchase the required number of reserved instances (Status Code: 400; Error Code: ReservedInstancesLimitExceeded; Request ID: 32762496-dfdf-447a-aff2-87cea127a11e) This isn't a very helpful error report because I only have one other instance, and my reserved instance limit is at 20, and I currently have no reserved instances. So what do I do to fix this?