The target version of the .NET Framework in the project does not match the .NET Framework launch condition version '.NET Framework 4'. Update the version of the .NET Framework launch condition to match the target version of the.NET Framework in the Advanced Compile Options Dialog Box (VB) or the Application Page (C#, F#).

This Warning i have experienced. When i going to change the Windows .Net Framework installer i had changed .Net Framework version 3.5 to version 4.0 that time i'm getting this issue. Its a easy to fix in this issue. Just Right click the setup solution explorer file and click the "view" and then click "Launch Conditions" the Issue founded.

and then Right Click the Launch Conditions "Properties Windows"

after that select the correct .Net Framework version

after that Right click the setup solution explorer file and select the properties

there is select on "Prerequsities" selection correct .Net Framework version.