Amir1986,   If you switch Openmanage Enterprise from Online to Offline, and then back to Online, it will clear the downloads.   Let me know how it goes.
I am running Open Manage Enterprise Version 3.9.0 (Build 55) No other plugins are now installed, I cannot remove, install or stop "Downloading" on this plugin [IMAGE]  
"Services" plugin stuck on "Downloading" and does not go away with reboot