are you missing a using directive or an assembly reference
<p>I can't figure out this error in visual c#.</p>

<pre>
Error   1
'Engine.VerticalMenu' does not contain a definition for '_buttons' and no extension method '_buttons' accepting a first argument of type 'Engine.VerticalMenu' could be found
(are you missing a using directive or an assembly reference?)   
</pre>

<p>For this line:</p>

<pre><code>System.Diagnostics.Debug.Assert(false, _menu._buttons.Count.ToString());
</code></pre>

<p>I have two projects, first one is Engine with same namespace Engine and of type class library, and the other one is windows form app that uses this Engine library. I have both using directives and references to project, what could possibly be causing this? Thank you.</p>
