I am new to development in dnn and I am attempting to build a new skin that works with codebehind.  I am working from a fresh install of dnn 7 but the site I am developing for is v5.6.  

To get started I found a very informative site that steps through each step, one of which is adding a reference for the dotnetnuke.dll. When I add the service reference I do so by pointing to the bin folder locally.  After completing all of the instructions, I am able to make the skin work and upon rebuilding, see changes being made locally.  This is where I run into trouble.  When I try to add it to the live site (dnn 5.6) it is throws an error and says the skin cannot be used because it was made for a newer version of dnn.  It then reverts to the default skin. 

After reading through some of the other forums that are related to this it says to use a relative path to add the reference such as ..\..\bin\ but Visual Studios does not allow this kind of reference adding.  My question is two fold, can I develop in the dnn 7 environment locally and push the skins to dnn 5.6?  If so, does anybody have any advice on how to get past this error or have any sources I can look at to accomplish this task? OR does anybody know of a resource for development that matches my environment?

Any help would be greatly appreciated.  Thank you.