I also tried launching cfbuilder 2 with -clean then tried installing again. Same issue.
The hotfix 1 is also installed.
Try to uninstall Hotfix 1, install the plugin and then reinstall hotfix 1. Maybe plygin installer checks the cheksums of these files and tries to update it from repository. However, threre no repositories added to CF Builder by default and it shows the error.
That worked. Thanks.