I am using .net 4.5 on IIS6.0 but am running Visual Studio 2015 … I could not find a library that seems to work with that. What would you suggest?
I would imagine a particular .NET Framework version is specified by your IIS installation. See this (which is for IIS 7,but I'm sure the similar exists for IIS6) https://technet.microsoft.com/en-us/library/cc754523%28v=ws.10%29.aspx
I can't help with IIS administration -- but I can say that you'll want to choose the Chilkat build that matches the .NET Framework version and the memory model (32-bit or 64-bit).
Also, make sure the VC++ redist runtime libs appropriate for the build are installed on the server.