The NSIS Error means that the downloaded installer file is either incomplete or modified from the original file.
It happens most often when the FrostWire installer is not downloaded from FrostWire's official website: www.frostwire.com or one of our official mirrors.
Just downloading it form our website, should fix the problem.
If the error still persists, here are some recommendations from: http://nsis.sourceforge.net/NSIS_Error
1. Clear your browser's cache.
2. Disable any download accelerators or managers and download the installer again.
3. Rename the installer so it is a simple one-word name with no special characters (without removing the .exe suffix)
4. Download the installer from another source approved by the software developer or publisher.
5. It might be corrupted on the server, or the connection to the server is unreliable from your location.
6. Update your anti-virus software (if installed) and download the installer again.
7. Disable your anti-virus software and download the installer again.
8. Download the installer using another computer and copy it to the original computer.
9. If you have the nVidia firewall installed, uninstall the program and download the installer again.
10. Scan for, and remove malware and viruses on your system.
11. Scan the hard drive using scandisk, chkdsk, or any other hard drive repair tool.
12. For people of ROMANIA who use FireFox in Romanian language try this tutorial: http://www.tutorialepc.ro/nsis-error-error-launching-installer-remediere-problema-2.html
13. Wait for Windows Update to finish updating drivers.