Zip program won't work!

I am using JZip. I cannot open any downloaded files from simviation as it tells me JZip does not recognize the format. I've never had this problem before. Is there anything anyone can suggest?
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=11&t=30862
I am the only user of this PC and yes I am logged on as Admin. I've never had to manually extract in to other files when downloading from other sites. I usually copy the new file straight into the FSX directory.
I tried extracting the files directly into the FSX/Simobjects/Aircraft directory and was told I do not have permission to write to that directory.