First off it depends on both the plugin and SketchUp version.
Many plugins are only for the Pro version of SketchUp and many plugins themselves require purchase.
Is your SketchUp Free or Pro?
What is the exact plugin?
Have you tried extracting outside of the program then importing?
And just by the way after your 40 day trial of WinZip is over it will no longer function without purchase.
Zip Genius is a forever Free program that is just as good.
ZipGenius.it - Free zip utility for Windows that handles zip, rar, cab, 7-zip archives and CD-ROM ISO9660 image files
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