I have seven projects in my solution, six of them are targeting .Net framework 4.5.2. The seventh one is referring the other projects and its targeting .Net framework 4.5. The reason it is like this is because few of the projects can be opened with another solution and they were upgraded.
When I build, I get an warning (actually Error window shows 0 errors / 0 warnings but status shows 'Build failed'. Output window shows many errors and warnings. Weird!) saying
"The primary reference project1.dll could not be resolved
because it was built against the ".NETFramework,Version=v4.5.2"
framework. This is a higher version than the currently targeted
framework ".NETFramework,Version=v4.5" (of Project7).
If you are importing a project file in csproj; make sure to remove the framework version tag in the imported project file.
Eg: If the parent project has import tag
<Import Project="test\ProjectBase.Files" />
Then in ProjectBase.Files remove the following tag