This is Adobe AIR's "catch all" error message. It can be caused by a variety of factors. To fix it, first try the Adobe steps to reinstall AIR. Make sure you're not running out of disk space and that you have sufficient permission to install--typically you need "Administrator."
If that doesn't work, installing with a different browser or clearing the browser cache often works.
When all else fails, here is a detailed Troubleshooting list for Error 5100. This covers some of the more hard-core fixes that can happen if there are registry problems or if malware from another source is blocking the install.
