I am using GitHub project repository for build trigger from Jenkins.
The intention is when even code push done in GitHub repository project my Jenkins build should
Couple of reasons for this to happen.
The neat little feature this provides is that it tests your connection with GitHub and provides you with the reason why it failed.
Hope this helps, took me a long time to figure this out :0
Either firewall is blocking or you've to check if WebHook is enabled in Github from Repository -> Settings -> WebHooks. There is a nice guide here. Use RequestBin for testing to make sure that its not a server side issue :)