The Unarc.dll error code 11 (often appearing alongside ISDone.dll) is a common decompression failure that occurs when installing large, highly compressed software like The Sims 4

Note: Remember to turn it back on after the installation is complete. 2. Increase Your Virtual Memory (Page File)

This is the most common fix. Antivirus software often flags the decompression of large game archives as suspicious behavior. Go to Windows Security > Virus & threat protection.

Your PC will restart and check for hardware issues. If it finds errors, you may need to replace a RAM stick or adjust your BIOS settings (like disabling XMP profiles temporarily). Final Tip: The "Short Path" Trick

The Fix:

If the archive itself is "CRC failed" or corrupted, no amount of system tweaking will fix it.