I can confirm this error on a very recent nova+ironic. While some nodes were failing deploy, I deleted and re-created the flavor to have less disk requirement, and now I cannot delete the instances:

+--------------------------------------+---------------------------------------------------------------------------------------------+
| Property                             | Value                                                                                       |
+--------------------------------------+---------------------------------------------------------------------------------------------+
| OS-DCF:diskConfig                    | MANUAL                                                                                      |
| OS-EXT-AZ:availability_zone          | nova                                                                                        |
| OS-EXT-SRV-ATTR:host                 | seed                                                                                        |
| OS-EXT-SRV-ATTR:hypervisor_hostname  | 772af6ac-d053-47cf-88b5-3cce94191bb4                                                        |
| OS-EXT-SRV-ATTR:instance_name        | instance-00000001                                                                           |
| OS-EXT-STS:power_state               | 0                                                                                           |
| OS-EXT-STS:task_state                | deleting                                                                                    |
| OS-EXT-STS:vm_state                  | error                                                                                       |
| OS-SRV-USG:launched_at               | -                                                                                           |
| OS-SRV-USG:terminated_at             | -                                                                                           |
| accessIPv4                           |                                                                                             |
| accessIPv6                           |                                                                                             |
| config_drive                         |                                                                                             |
| created                              | 2014-12-11T10:27:04Z                                                                        |
| fault                                | {"message": "Flavor 7 could not be found.", "code": 404, "created": "2014-12-11T10:37:51Z"} |
| flavor                               | baremetal (82f959f5-b20e-44b2-9604-f68abc19e214)                                            |
| hostId                               | e7fd3fa395a116811e038357c0c1fc0f37af09d8c600294e1631a1d6                                    |
| id                                   | 44a7bb32-9563-492a-b20e-1354193651d2                                                        |
| image                                | overcloud-compute (6250ce83-56f6-4b5f-8bcd-d3f170b9b7ae)                                    |
| key_name                             | default                                                                                     |
| metadata                             | {}                                                                                          |
| name                                 | ci-overcloud-NovaCompute0-rwvmd5ld5p7k                                                      |
| os-extended-volumes:volumes_attached | []                                                                                          |
| status                               | ERROR                                                                                       |
| tenant_id                            | 6c7831f11fc944ce89fdfe09205f1f7d                                                            |
| updated                              | 2014-12-11T10:37:51Z                                                                        |
| user_id                              | 74c6f23f576544fcad95de5498dada0d                                                            |
+--------------------------------------+---------------------------------------------------------------------------------------------+