Even though the release is not listed under JMX getAllActiveReleases the release id of such release can be obtained from ROC UI and can be removed via JMX. Please find step below to do the same.
1: Login to ROC
2: Navigate to the erroneous release and obtain the release id from address bar
3: Navigate to JMX (http://<NAC hostname>:20203).
4: Login with username/password default
5: Scroll down to the section "Domain: releasecenter".
6: Select "releasecenter:type=Info".
7: Invoke the method removeRelease
passing the release id capture in step 2. For example in above case it will be 7. The erroneous release will be removed.