@zupidupi, did you download that file from this site? Which package is that? Maybe the file is corrupted during download or is simply a bad .package file.
Have you tried with another .package file?
If it cannot recognize any .package file, I believe the culprit is the Resource.cfg file, in which case you'd need go through the wiki again and to redownload that .cfg from here
I've tried other packages and none work. I've tried with that resource file and nothing.
Looks like something is wrong with your .cfg file if all custom content are not showing. Could you post the contents of your resource.cfg file? I doubt it's that boots package as others seem to be using it fine.
1. Are you installing with the game running? Game cannot be running when installing new stuff.
2. Are you on Vista? There's a specific UAC version of the Installer Helper for Vista users with UAC issues. Read the thread there, the solution for you might be available there.
3. Are you doing a right-click on the .package file to install it while the file is already in C:\Programas\Electronic Arts\Os Sims 3\Mods\Packages\ path? How about cut+paste that boots .package to desktop, right-click and install it again?
4. Can you test with the no musical notes mod or no red line mod )? Simple and visibly easy to test...can you still see musical notes when playing instruments or the red line when paused?
5. Have you remove the *Thumbnails.package from \My Documents\Electronic Arts\The Sims 3\Thumbnails ? (necessary to force the game to generate new thumbnails if you install new objects or textures/patterns)
report back which steps work/don't work for you...gd luck!