Usually it's due to SSL compatitable issue.

Check the log fil of netbeans first according to this FAQ =>http://wiki.netbeans.org/FaqLogMessagesFile

And then following by these three steps.

1.Install unlitimate policy keys for jre
for java 7 =>http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html
for java 8 => http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html
Get "local_policy.jar" and "US_export_policy" , to replace the ones under /lib/security

2.If step1 doesn't help , then it could be the ssl certificate validation issue.
Install this plugin http://plugins.netbeans.org/plugin/53877/ssl-certificate-exception
So that you can accept invalid ssl certificate on netbeans , sometime it's not because your certificate is really invalid , it's just because java client can't download the valid intermedia/root CA.

3.Still doesn't help? did you build up your own git server with 2048 bits DH param ?
If yes , downgrade it to 1024 bits , because some java envirounment doesn't support DH param over 1024bit.
In this case , error message in the log file will be "java.security.InvalidAlgorithmParameterException: Prime size must be multiple of 64, and can only range from 512 to 2048"