The "Unarc.dll error code -6" during a FIFA 13 installation is almost always tied to file corruption, permission blocks, or memory restrictions. Starting with administrative privileges and disabling your antivirus will fix the majority of occurrences. If the problem persists, increasing your virtual memory or redownloading the setup file from a clean link will ensure a successful installation.

The decompression tool uses substantial virtual RAM memory. If your virtual memory limit is too low, the extraction drops mid-way.

However, if you are using a or "Portable" version of FIFA 13 (not an installer), this error will never go away. You must download a proper repack (FitGirl, DODI, or ElAmigos).