www.jfileupload.com

I have upload applet on the site running and working fine before installing SSL certificate.But recently I installed SSL certificate on the website. Now the applet is giving the following error
Upload started ...Upload failed : javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

It means your certificate it not trusted (self-signed) or signer is not found in trust store. you can bypass this check by installing WeakSSL add-on:
http://www.jfileupload.com/products/tools/index.html