title: CS8001: SDK path could not be resolved after compiling C# app on Ubuntu 16.04
body: <p>After searching around the web, <a href="https://stackoverflow.com/questions/35617920/csharp-error-on-ubuntu-14-04">this </a> ask Ubuntu question, and <a href="https://stackoverflow.com/questions/35617920/csharp-error-on-ubuntu-14-04">this</a> Stack Overflow question, I'm having no luck in figuring out why I'm getting this warning after compiling a simple C# command line app via terminal. I'm using mono, and after </p>
  
  <pre><code>dmcs myProgramName.cs
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>warning CS8001: SDK path could not be resolved
  Compilation succeeded - 1 warning(s)
  </code></pre>
  
  <p>I read that Ubuntu 12.04 and 14.04 depends on libmono-winforms2.0-cil, but after trying to install that with</p>
  
  <pre><code>sudo apt-get install libmono-winforms2.0-cil
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>Package libmono-winforms2.0-cil is not available, 
  but is referred to by another package
  This may mean that the package is missing, has been obsoleted,
  or is only available from another source
  However, the following packages replace it:
  mono-reference-assemblies-2.0 mono-devel
  </code></pre>
  
  <p>Through more searching, I read that libmono-system windows-forms4.0-cil is what I need for Ubuntu 16.04, but after trying to install it I get</p>
  
  <pre><code>libmono-system-windoes-forms4.0-cil is already the newest version
  </code></pre>
  
  <p>Does anyone have any suggesstions on how to trace this compilation warning? I've reached a dead end.</p>