user26965: Whenever I compile a sketch, change the Tools > Board selection, or open/close Boards Manager/Library Manager I get the following message in the console:
> WARNING: Spurious .github folder in 'Adafruit Motor Shield library' library 
> WARNING: Spurious .github folder in 'Adafruit Motor Shield V2 Library' library
> 
> 
> Invalid library found in
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master:
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
> Invalid library found in C:\arduino-1.6.8\libraries\robotarm:
> C:\arduino-1.6.8\libraries\robotarm Invalid library found in
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master:
> C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
> Invalid library found in C:\arduino-1.6.8\libraries\robotarm:
> C:\arduino-1.6.8\libraries\robotarm


user26916: Arduino IDE 1.6.6 and higher are picky about what you have in your libraries folders. There are two general valid library formats, the old "pre-1.5" format and the newer 1.5 format, the specification of which is at https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification.
Any folder in any of the Arduino libraries folder that doesn't follow a valid library format will cause the "Invalid library" message. Common causes of this issue are:

Putting a sketch folder in the libraries folder. Libraries may
contain example sketches but a sketch by itself is not allowed.
Libraries that are in a subfolder, rather than the library folder
being in the root of the libraries folder as required.

Now lets look at your specific messages:
Invalid library found in C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master: C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master

By looking at the Adafruit-Motor-Shield-for-Arduino repository we see that it's not a library but the PCB design files for the shield and thus has no business being in the libraries folder. Please move it to a different location.
Invalid library found in C:\arduino-1.6.8\libraries\robotarm: C:\arduino-1.6.8\libraries\robotarm

Without being able to see what's in this folder I can't say exactly the problem. If you will provide a directory listing I could update this answer with specific directions. As it is now, that folder is doing you no good in the libraries folder.

26965: <p>Whenever I compile a sketch, change the <strong>Tools > Board</strong> selection, or open/close Boards Manager/Library Manager I get the following message in the console:</p>

<pre><code>&gt; WARNING: Spurious .github folder in 'Adafruit Motor Shield library' library 
&gt; WARNING: Spurious .github folder in 'Adafruit Motor Shield V2 Library' library
&gt; 
&gt; 
&gt; Invalid library found in
&gt; C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master:
&gt; C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
&gt; Invalid library found in C:\arduino-1.6.8\libraries\robotarm:
&gt; C:\arduino-1.6.8\libraries\robotarm Invalid library found in
&gt; C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master:
&gt; C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
&gt; Invalid library found in C:\arduino-1.6.8\libraries\robotarm:
&gt; C:\arduino-1.6.8\libraries\robotarm
</code></pre>
 26916: <p>Arduino IDE 1.6.6 and higher are picky about what you have in your libraries folders. There are two general valid library formats, the old "pre-1.5" format and the newer 1.5 format, the specification of which is at <a href="https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification" rel="nofollow">https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification</a>.</p>

<p>Any folder in any of the Arduino libraries folder that doesn't follow a valid library format will cause the "Invalid library" message. Common causes of this issue are:</p>

<ul>
<li>Putting a sketch folder in the libraries folder. Libraries may
contain example sketches but a sketch by itself is not allowed.</li>
<li>Libraries that are in a subfolder, rather than the library folder
being in the root of the libraries folder as required.</li>
</ul>

<p>Now lets look at your specific messages:</p>

<pre><code>Invalid library found in C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master: C:\arduino-1.6.8\libraries\Adafruit-Motor-Shield-for-Arduino-master
</code></pre>

<p>By looking at the <a href="https://github.com/adafruit/Adafruit-Motor-Shield-for-Arduino" rel="nofollow">Adafruit-Motor-Shield-for-Arduino repository</a> we see that it's not a library but the PCB design files for the shield and thus has no business being in the libraries folder. Please move it to a different location.</p>

<pre><code>Invalid library found in C:\arduino-1.6.8\libraries\robotarm: C:\arduino-1.6.8\libraries\robotarm
</code></pre>

<p>Without being able to see what's in this folder I can't say exactly the problem. If you will provide a directory listing I could update this answer with specific directions. As it is now, that folder is doing you no good in the libraries folder.</p>
