If Visual Studio 2005/2008 encounters a problem with an addin it will disable it by altering the addin xml.

To enable the addin again ensure the addin xml is in the "\document\visual studio x\addin\" folder, as per the installtion guide, and ensure the following settings are in the .addin xml

 <LoadBehavior>5</LoadBehavior>

<CommandPreload>1</CommandPreload>

<CommandLineSafe>1</CommandLineSafe>

=========================================================================
THE Visual Micro SOFTWARE IS PROVIDED TO YOU "AS IS," AND WE MAKE NO 
EXPRESS OR IMPLIED WARRANTIES WHATSOEVER WITH RESPECT TO ITS 
FUNCTIONALITY, OPERABILITY, OR USE, INCLUDING, WITHOUT LIMITATION, ANY 
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, 
OR INFRINGEMENT. WE EXPRESSLY DISCLAIM ANY LIABILITY WHATSOEVER FOR ANY 
DIRECT, INDIRECT, CONSEQUENTIAL, INCIDENTAL OR SPECIAL DAMAGES, 
INCLUDING, WITHOUT LIMITATION, LOST REVENUES, LOST PROFITS, LOSSES 
RESULTING FROM BUSINESS INTERRUPTION OR LOSS OF DATA, REGARDLESS OF THE 
FORM OF ACTION OR LEGAL THEORY UNDER WHICH THE LIABILITY MAY BE ASSERTED, 
EVEN IF ADVISED OF THE POSSIBILITY OR LIKELIHOOD OF SUCH DAMAGES.
=========================================================================

===========================================================
Version: 1004.11
Copyright: Visual Micro 2010

For licence and usage guide see http://www.visualmicro.com.
This readme file must be included with Visual Micro.
===========================================================

-------
Summary
-------

The Visual Micro add-in for Microsoft Visual Studio requires the Arduino 
software environment. The Arduino software is free and can be obtained 
from http://arduino.cc.

The Visual Micro add-in (also known as Visual Micro for Arduino) has not 
been approved or acknowldged by the Arduino creators.

This software is free of charge for personal and educational use only.

-----
Setup
-----

After installation, make sure the Visual Studio add-ins folder is 
present, and manually copy the Visual.Micro.Visual.Studio.Arduino.AddIn 
file to this directory.

The default location for the Visual.Micro.Visual.Studio.Arduino.AddIn 
file is:

   C:\Program Files\Visual Micro\Visual Micro for Arduino\

The default location for the Visual Studio add-ins folder is:

   (Visual Studio 2008 : XP)
   %ALLUSERSPROFILE%\Application Data\Microsoft\MSEnvShared\AddIns

   (Visual Studio 2010 : XP)
   %ALLUSERSPROFILE%\Microsoft Visual Studio\Addins

If you did not install Visual Micro into the suggested default location 
you will need to edit the *.AddIn XML file to reflect the location of 
your installation:

   <Addin>
     ...
       <Assembly>..\Visual Micro\Bin\Visual.Micro.Visual.Studio.Arduino.dll</Assembly>
     ...
   </Addin>

   <ToolsOptionsPage>
     ...
       <Assembly>..\Visual Micro\Bin\Visual.Micro.Visual.Studio.Arduino.dll</Assembly>
     ...
   </ToolsOptionsPage>

To disable Visual Micro you can:

1) Uncheck the add-in in Visual Studio's Add-In Manager;
2) Remove the *.AddIn file from Visual Studio's add-ins folder;
3) Set the <LoadBehavior> property in the *.AddIn file to '0'.

The default <LoadBehavior> = 5 causes the add-in to load in Visual 
Studio. If you alter the <LoadBehavior> property you will need to restart 
Visual Studio for the change to take effect.

--------------------
Visual Micro Options
--------------------

In Visual Studio you can specify the Arduino & AVR-GCC paths in the 
Visual Micro options:

   (Tools|Options|Visual Micro)

   [Locations]
   Arduino Application:  ..\Arduino
   Arduino Library    :  ..\Arduino\libraries
   GCC Application    :  ..\Arduino\hardware\tools\avr\bin
   Include Locations  :  < VS 2010 Intellisense Include Paths >
   Sketch Folders     :  ..\My Documents\Arduino

   [Projects]
   Allow Compile:  True
   Allow Upload :  True
   Allow Create :  True
   Allow Open   :  True

You can compile simple shetches at the moment, but if a sketch references 
another sketch then you may have problems. 

In Arduino options you can check "Use external editor", this makes 
Arduino reload the entire sketch prior to compilation, so you can edit in 
Visual Studio and compile in Arduino quite easily.

---------------------
Visual Studio Options
---------------------

In Visual Studio you can associate the *.pde extension with Visual C++:

   (Tools|Options|Projects and Solutions)

   [VC++ Project Settings]
   C/C++ FIle Extensions:  *.cpp;*.cxx;*.cc;*.c;*.pde
   Extensions To Include:  .cpp;.cxx;.cc;.c; ... ;.manifest;.pde

   (Tools|Options|Text Editor)

   [File Extension]
   Extension:  PDE
   Editor   :  Microsoft Visual C++

You can also tell Windows to treat *.pde files as C++ *.cpp files by 
editing the registry. Save the text below to a *.reg file and execute it:

   Windows Registry Editor Version 5.00

   [HKEY_CLASSES_ROOT\.pde]
   @="CPPFile"

---------
Uninstall
---------

Uninstall Visual Micro via Windows Control Panel|Add/Remove Programs, and 
manually delete the *.AddIn file.

If necessary, you can clear all Visual Studio commands created by Visual 
Micro with the "/resetaddin" switch:

   ..\Microsoft Visual Studio 9.0\Common7\IDE\devenv.exe /resetaddin Visual.Micro.Visual.Studio.Arduino.Helper

Instead of using the switch, you can also set the "Installed" property to 
"False" prior to uninstalling the software:

   (Tools|Options|Visual Micro)

   [User Interface]
   Installed:  False 

There are two settings to apply when configuring an arduino sketch to be recognized in visual studio as a c++ file. Both settings are accessed in visual studio via tools>options

Register pde (sketch) as a C++ file allowing both intellisense and code formatting to be displayed/applied

The initial release of the visual micro addin for visual studio is designed for arduino however it should be possible to use the system to program normal avr devices using visual studio. This is entirely untested but at the very leat this software will provide all the information and tools you need to adapt an avr solution.

Ignoring the arduino boards and library system you will find everything you need to adapt your own Visual Studio avr solution. AVR Intellisense, compliation, upload and much more