1. Check the release note of the version you are attempting to install for the prerequisite requirement(s) for installation. Usually this can happen if the Operating System is not supported or required patches are not installed.
2. Verify there are no spaces in the folders or directory structure of the installer. For example, you cannot put the installer in C:/Spectrum Installs/Spectrum. You would need to remove the space: C:/Spectrum_Installs/Spectrum
3. You are installing a version of Spectrum that requires a previous version. For instance, if you are installing 10.4.3.1 (aka 20.2.10) you must install 10.4.3.0 first (20.2.7). If you do not install 20.2.7 first the selection is grayed out for the 20.2.10 install.