It means that you have an older model of CPU that does not support all instructions Corona uses. Up to Corona 1.7 hotfix 2, you can still use a legacy build, which the installer will install automatically. It offers the same features and is fully compatible with the regular build but is a bit slower.
From Corona 2 onward, the legacy version will no longer be offered, and you will need a CPU that supports the SSE4.1 instruction set (that is, any processor from within the last 10 years). Here is a list of compatible CPUs.
From Corona 3 onward, the Corona Licensing Server will no longer support CPUs without the SSE4.1 instruction set and is now a 64-bit only application (It will not run on 32-bit versions of Windows).