Created attachment 916708 [details]
Logs from production.log

Description of problem:
I was trying a specific scenario to delete to a CV. I created a CV and published it and promote it to next env. Later, I created a new activation-key and selected same cv. Now when I tried to delete CV, UI says: To delete CV, first remove its version and move the associated entities (activation-key) to other CV or env. I followed same and removed the version. On removing the CV version, UI raises notification:

"Successfully initiated removal of testcv2 version 1."

After above notification, I tried to remove the CV and got following error on UI:

Required lock is already taken by other running tasks. Please inspect their state, fix their errors nad resume them. Required lock: read Conflicts with tasks: - https://dhcp207-190.lab.eng.pnq.redhat.com/foreman_tasks/tasks/1b44ce3f-c919-4b87-af1c-3b9701948f69 


Version-Release number of selected component (if applicable):
Satellite-6.0.3-RHEL-6-20140626.1

How reproducible:
always

Steps to Reproduce:
1. create a CV (cv1), publish it and promote it to next env (dev)
2. create activation-key(ak), select 'dev' env and 'cv1' 
3. Now try to delete CV
4. first UI will sk to delete its version.
5. Once you triggered version deletion, immediately try to delete CV too

Actual results:
UI raises:

Required lock is already taken by other running tasks. Please inspect their state, fix their errors nad resume them. Required lock: read Conflicts with tasks: - https://dhcp207-190.lab.eng.pnq.redhat.com/foreman_tasks/tasks/1b44ce3f-c919-4b87-af1c-3b9701948f69 

Expected results:
UI should raise proper message, saying that deletion is still on-going or something like that and log shouldn't be filled with 500 ISE

There are several other cases, related to locking, and all needs to be handled properly.

Additional info: