Problem
When trying to add a new server to the Package and Deployment tool, the following error appears:
This BackgroundWorker is currently busy and cannot run multiple tasks concurrently.
The Create New Package, Edit Package and Deploy Package are also disabled which is expected as there is no Server listed.
Solution
A possible cause is that port 5555 is blocked on the server. Port 5555 is the default port through which package and deployment connects to the K2 server.
Please see if you are able to successfully telnet to the server on port 5555. If that is successful, then please try to perform a K2 service restart and IISRESET on the server. If you have multiple servers in a Farm setup, please do so all server nodes in the environment.