Hi Namitha,
This occured because the internet connection was slow so the eclipse zip file you downloaded was not complete .So it was corrupted.I faced the same problem and tried to re-download and it worked.If that also does not work .You can use any eclipse which is already istalled on your system and configure it for JBPM by installing the necessary plugins. You can extract the zip file(org.drools.updatesite-5.3.1.Final-assembly) that comes with JBPM full installer zip file.You will find two folders plugins and features .Copy the corresponding jar files and paste it in your eclipse's plugins and featues folder and restart your eclipse.