Unarc.dll or Isdone.dll errors are quite common for both Windows 7 and Windows 8 (8.1) users. The fact is, they are almost one and the same error. These errors can occur when you, for example, download an archive from the Internet and try to unpack it, or try to install a downloaded game with the Innosetupinstallation program.

First thing to try: disable your antivirus and try running the program again. If that works, scroll to the bottom of the page and use the share buttons.

Second: if the path to the file that won’t run has non-latin characters in it, move file to another location, to C: root folder, for example.


If you search for a fix on the Internet, you’ll find many “unarc.dll fixer” programs, but none of them work. I highly recommend that you not download any of these applications. Working for quite a while as an IT support engineer, I can give you some helpful advice on how to fix the unarc.dll and Isdone.dll errors.

Common error messages for unarc.dll and Isdone.dll

  • An error occurred while unpacking: archive corrupted unarc.dll returned an error code: 1, 6, 7, 12 error: archive data corrupted (decompression fails)
  • ISDone.dll error
  • An error occurred while unpacking: archive corrupted!
  • Unarc.dll returned an error code: 7
  • Unarc.dll returned an error code: 6
  • Unarc.dll returned an error code: 12
  • Unarc.dll returned an error code: 1
  • ERROR: archive data corrupted (decompression fails)

The error may happen during the installation of Resident Evil, Crysis Warhead, Day One, Assassin’s creed and other games.

Try the software on another PC

These steps may seem strange, but you should try them if you really want to fix the error:

  • Move the file from the computer on which the error occurred to another PC. (Use a USB flash drive or local network. Do not just download it from the same source on the Internet.)
  • If the file works, then something is wrong with the first PC. There may be several causes of the problem. For example, there might be system or RAM issues.
  • If there’s still an error on another PC, try the same file, directly downloaded to the second computer from the same source on the Internet. Try unpacking or installing it.

If the result is: “Wow! It worked on the second PC! How can that be?” then you should strongly consider RAM problems on the first machine, as this is a very likely cause. For some reason unarc.dll and Isdone.dll errors are most often caused by hardware issues, and are not Windows 7 or Windows 8 problems.

If neither troubleshooting method worked, we should deal with the source of the file. If possible, try another source for the program. If not, you may try usingUniversal Unpacker free software, which you can easily find on the web. With this utility, it’s sometimes possible to unpack installation packages that seem to be corrupted.

Fixing unarc.dll error caused by RAM problems


If you come to conclusion that your RAM is the cause of the unarc.dll error, then the only thing I can suggest is to remove memory modules one by one (don’t do it if you don’t know how) and test the program again. If you find it works when a specific RAM module is removed, you will have found the problem.