Thank you for your post.
Your best bet would be to contact the company that created the "FM-iCal-Connector" plug-in. They are the ones most familiar with what needs to be accomplished to make this work with FileMaker Pro.
Even though we are not familiar with the plug-in, you can talk with a Technical Support specialist. If you are in North America, please call toll-free 800-325-2747.
I appreciate your feedback. I have contacted the third-party company. I stand to try to find help from Filemaker users as well.
In addition, I have contacted technical support. They were unable to help.