R – How to solve: Custom MSBuild task requires assembly outside of AppBase

The root of your problem is that the assembly Macrovision.InstallShield.Tasks.dll is type-unsafe (managed and native code mixed / IJW) and runs for x86 architecture only. Macrovision has failed here to do nice interop assembly modularisation for specific architectures. Tasks in Macrovision.InstallShield.Tasks.dll depend on native tools to build an MSI package. These native tools are only available for x86 architecture, hence the dependency.

Macrovision should have made a type-safe (AnyCPU / PURE) tasks assembly for MSBuild and deploy architecture specific code and calls into interop assemblies for specific architectures, most prominently x86 and AMD64. This way, any flavor of MSBuild or any other consumer of the tasks assembly would work (of course, as far as specific interop assemblies for a given architecture exist).

Probably the best way to get around your problem is to compile your project as AnyCPU and execute a 32-bit MSBuild. Or start a 32-bit CLR or process and then consume Macrovision's assembly.

If you target the Framework version you want to be compatible with instead of targeting 3.5, Visual Studio 2008 SP1 and FxCop 1.36 RTM added rule CA 1903: Use only API from targeted framework to ensure you stay compatible with the target framework version. Turning that rule on and treating it as an error will fail your Build and provide the behavior you want.

Here is sample code demonstrating a violation when you are targeting framework version 2:

using System.Runtime;

class Program
{
    static void Main()
    {
        GCSettings.LatencyMode = GCLatencyMode.LowLatency;
    }
}