What are you trying to do ??
Please read the full guidance notes.
Simple checklist...
You need a model with a PNG image installed, which has some transparent pixels which get deleted. It also needs the the other solid pixels to have no transparency at all.
You need the SKMtools installed to give you ImagerTrimmer.
ImageTrimmer uses some java applets [.JAR files] to do image manipulation.
You need JAVA installing to use them.
Some people get problems because the compression-app is set to open them.
Also [as it appears in your case] you CANNOT have the .jar file-type extension associated with any other program.
Perhaps in your case looks like it's been given over to something like WinRar.
When you install some compression/decompression programs the default set of file-types which they are set up to open often includes .jar - which is actually a re-suffixed ZIP file - just like a SKM, Style or Layout file.
To stop this happening, open WinRar's preferences and un-check [unassociate] that .jar file-type, save changes and close WinRar.
Now retest ImageTrimmer in SketchUp and see if the .jar applets execute properly [rather than open]...
If you set the JAR files to open in SketchUp it will not work - so delete that option.