This error means that the installation files are corrupted.
There are several reasons why this may happen:
Your system might be unstable or an application might be interfering with the installation process. Reboot your computer and try installing the game again. If the issue persists try the Troubleshooting with MSconfig method to see if a program or background process is interfering with the download.
Your Temporary Internet Files may need to be cleared.
For Internet Explorer users: Click on “Tools”, select “Internet Options” and click on “Temporary Internet Files” (or “Delete…”) from the “General” tab. Select “Delete Files”.
For Firefox users: Click on “Tools”, select “Clear Private Data” and then click on “Clear Private Data Now”.
This may take several minutes. Once it’s done, download MapleStory.
Your download manager could be corrupting the downloaded files. If you have a software that you use to manage or accelerate your downloads, we suggest that you turn it off and download MapleStory without it.
You can also uninstall MapleStory and make sure all files and folders are deleted and then download the Nexon Launcher.