I have a VS 2012 web project /sln that I am trying to build in TeamCity. it uses .NET 4.5 which is installed on TeamCity.
The TeamCity server has VS 2010 in
Firstly, TeamCity does not require presence of Visual Studio of any version to build. When a build step in the project is configured with MSBuild runner TeamCity needs to know which version of MSBuild to use. This is a setting of a build step. Proper MSBuild version must be selected in a build step configuration according to the .NET tools installed on a build machine. TeamCity will use that value to determine the location path and will set an environment variable when invokes MSBuild.
The problem with the Visual Studio 2012/2013 is that it's only supported by TeamCity starting 8.1.0. So if your TeamCity version is before 8.1. you need to upgrade to the latest 8.1.x to see a setting for MSBuild Tools 2013. Once you select a proper MSBuild version in the build step settings the problem will disappear. For more information read here: http://blog.turlov.com/2014/07/upgrade-teamcity-to-enable-support-for.html