This may likely be due to some local HTTP proxy setup problem.
To solve this you can try the following:
Window->Preferences->General->Network Connections->
Provider: Manual
(where Eclipse proxy settings are applied)- (adjust proxy rules as desired) (try including/excluding rules matching your jasper server host)
- restart Eclipse (important!)
I found this solution a little hidden here: Jasper forum question 3143 comment 16.