ISDone.dll and its companion unarc.dll do one job: unpack the heavily compressed archives inside a game installer. When you see this error, the installer failed mid-unpacking - and the cause is almost never a missing DLL. It is the archive being damaged, the antivirus interfering, or the PC running out of memory or disk during decompression. That is why downloading ISDone.dll from a site never fixes it - the file was fine, the unpacking was not.
Fix it automatically
Outbyte PC Repair checks Windows for corrupted system files, registry problems and leftovers from removed programs - the kind of damage behind errors like this one. Useful when you would rather not run the steps below by hand - the check and the diagnosis are free, and nothing is changed until you decide.
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Three things fix most ISDone errors: free up disk space (the game needs room for both the archives and the unpacked files), add the installer folder to the antivirus exclusions for the duration of the install, and re-download the installer if the error repeats at the same percentage - that is a damaged archive.
An interrupted or slightly corrupted download breaks the compressed archive - unpacking then fails at the exact same spot every time. Only a fresh download cures it.
Real-time scanning locks or removes files while the installer writes thousands of them - unpacking errors with random codes are the result.
Heavily compressed installers need several gigabytes of working room beyond the final game size, and low memory kills the decompressor with error codes -1 or -7.
Decompression is one of the most memory-intensive things a home PC does. An aggressive XMP profile or a failing module shows up here first - error codes differ between attempts.
Honest note: only do this for an installer from a source you trust. If you are not sure where the installer came from, the antivirus stopping it may be the best outcome.
No - those files are part of the installer itself and they are not broken. The error is the unpacking failing around them: damaged archive, interference, or lack of resources. A downloaded DLL changes nothing except adding risk.
That is the signature of a damaged archive: unpacking reaches the broken block and dies there every time. Only re-downloading the installer helps.
Big installers use extreme compression to cut download size. Unpacking them is heavy on RAM and disk, so marginal hardware problems and space shortages surface exactly here.
Outbyte PC Repair checks the system and shows what it found - then waits. Nothing is applied without your OK, and a restore point lets you undo changes.
Download PC Repair Downloads Outbyte PC Repair for Windows. Free by-category trial included.