We've heard of this issue only once before but have been unable to diagnose where the problem is coming from due to lack of details.
Can you help explain when you see this error? Is it right after you try to upload and install? Does it look like the installation was successful (success should show a long table detailing what was and wasn't installed with JFBConnect). If it seems successful, are you able to go to Components -> JFBConnect in the admin area and configure options?
Any more details you can provide on the state of your site after the installation will really help us narrow down what could be wrong and how to proceed.
Thanks,
Alex