I wanted to share something that seems to be working for me as a workaround to this problem.  I am not a developer, but I often find myself interested in or tasked with solving crazy issues like this that have no immediate solution or workaround.  Sometimes that involves working with code, but I wanted to emphasize that I'm more of an admin by trade rather than a programmer, so I'm mostly putting this out there to see what others think about it.

The issue seems to occur when Outlook tries to initialize various callbacks in the IRibbonControl interface.

Add-in execution error. Outlook crashed during the 'GetVisible' callback of the 'IRibbonControl' interface while calling into the 'Salesforce.com Outlook Edition Enhanced' add-in.

As I understand, there were some changes in terms of how custom ribbons should be coded between Outlook 2007 and 2010.  My theory here is that thecallback code that has been written to implement the Salesforce ribbon (when called from xml) isn't compatable with 2010, and Office is by design supposed to check add-ins when it opens and crash immediately if there's a problem with any of them.

Easy enough to figure out which dll we're dealing with..

If we open that dll with Visual Studio 2010 we can expand String Table and double click it to edit it.

Copying that, pasting it in an editor, and doing some basic structuring gives us:

<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui" loadImage="LoadRibbonImage" onLoad="OnRibbonLoad">   
 <ribbon>       
  <tabs><!-- Note: The button id's must be the same as in GlobalDefs.h so they can be turned off with reg keys -->           
   <tab id="SFDCTab" label="Salesforce.com" getVisible="GetVisible">               
   <group id="EmailGroup" label="{EMAIL_GROUP_LABEL}" getVisible="GetVisible">                   
   <button id="SendAddMail" size="large" label="{SENDADD_LABEL}" screentip="{SENDADD_LABEL}" supertip="{SENDADD_TIP}" image="SendAdd56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />                   
   <button id="AddressBook" size="large" label="{ADDRBOOK_LABEL}" screentip="{ADDRBOOK_LABEL}" supertip="{ADDRBOOK_TIP}" image="AddressBook56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />                   
   <button id="AddMail" size="large" label="{ADDEMAIL_LABEL}" screentip="{ADDEMAIL_LABEL}" supertip="{ADDEMAIL_TIP}" image="AddEmail56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />                   
   <button id="CreateCase" size="large" label="{CREATECASE_LABEL}" screentip="{CREATECASE_LABEL}" supertip="{CREATECASE_TIP}" image="CreateCase56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />        
   </group>               

   <group id="ItemGroup" label="{ITEM_GROUP_LABEL}" getVisible="GetVisible">                   
   <button id="SaveMarkSync" size="large" label="{SAVEMARK_LABEL}" screentip="{SAVEMARK_LABEL}" supertip="{SAVEMARK_TIP}" image="SaveMark56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />              
   </group>
               
   <group id="AssociationsGroup" label="{ASSOCIATIONS_GROUP_LABEL}" getVisible="GetVisible">                   
   <button id="Associations" size="large" label="{ASSOCIATIONS_LABEL}" screentip="{ASSOCIATIONS_LABEL}" supertip="{ASSOCIATIONS_TIP}" image="AcctLookup56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />
   <button id="View" size="large" label="{VIEW_LABEL}" screentip="{VIEW_LABEL}" supertip="{VIEW_TIP}" image="View56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />                   
   <button id="Who" size="normal" getLabel="GetLabel" getScreentip="GetScreentip" getSupertip="GetSupertip" image="View56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />                   
   <button id="What" size="normal" getLabel="GetLabel" getScreentip="GetScreentip" getSupertip="GetSupertip" image="View56x56.png" getEnabled="GetEnabled" getVisible="GetVisible" onAction="ButtonClicked" />               
   </group>           
   </tab>       
  </tabs>   
 </ribbon>
</customUI>

If we trash most of that, leaving in only say the <customUI> tag, and save the dll, when Outlook loads the add-in, it doesn't have what it needs to try to implement it as a ribbon, and throws the normal buttons under the Add-Ins tab like a legacy add in or custom button.

It's not as pretty and versatile as it is when implemented as it's own ribbon control, but all of the functions I've tested so far work exactly as they should.  Anybody else have any thoughts on this?  I know it's a bit of a hack, but if you keep it from loading as a custom ribbon it seems to work :-)