getting an ISDone.dll error when trying to install a game. the error message says something about ‘an error occurred while unpacking’ and mentions Unarc.dll.
the game is large (around 40GB). the installation gets partway through then fails with this error. tried running the installer as administrator and got the same result.
what is ISDone.dll actually doing and why does it fail? and what’s the actual fix sequence? i’ve seen suggestions ranging from reinstalling visual C++ redistributables to checking RAM, but i don’t know which of those is actually the cause versus people just throwing suggestions.
Insufficient RAM being the most common cause is accurate and often overlooked. Modern browsers with multiple tabs can use several gigabytes of RAM. Running a large game installer with Chrome open and multiple tabs is asking for ISDone.dll failures. Closing everything and restarting before installation is the simple prevention.
the restart before installing approach works because it clears all running background processes and gives you maximum available RAM from a clean state. installing right after a restart rather than after hours of use dramatically reduces ISDone.dll errors on systems with 8gb or less of RAM.
re-downloading the installer being the fix for some cases is something people are reluctant to do when the file is large. but a partial or corrupted download causes exactly this error with no way to fix it on the system side. verifying the download size against what the site says is the quick check before re-downloading.
ISDone.dll handles decompression during installation for installers built with InnoSetup. the error means the decompression process failed, usually for one of a few reasons.
most likely causes and fixes in order:
RAM issue: large game installations decompress into RAM. if you have insufficient free RAM or faulty RAM, decompression fails. close everything else before installing. if you have under 8GB RAM, this is more likely. run windows memory diagnostic (windows search > memory diagnostic) to check for RAM errors.
corrupted download: the installer file itself may be partially corrupted. if you downloaded it, re-download and verify the checksum if the source provides one.
missing or corrupted Visual C++ redistributables: ISDone.dll depends on these. go to control panel > programs > look for Microsoft Visual C++ Redistributable packages and repair or reinstall them. download the latest versions directly from Microsoft.
insufficient disk space: the installation needs space both for the final install and temporary decompression space. you may need significantly more free space than the final game size. check that your system drive (usually C:) has at least 20-30GB free even if the game installs elsewhere.
run the installer as administrator: right-click > run as administrator ensures it has write access for temporary files.
try these in order. the RAM and download corruption causes account for most ISDone.dll failures on large game installations.
The temporary disk space requirement being on the system drive is a specific detail that catches people who install to a secondary drive. They check that D: has enough space but the system drive C: is nearly full. The installer needs temp space on C: regardless of the install destination.