Error occurred in deployment step ‘Activate Features’: Operation is not valid due to the current state of the object

SharePoint 2010 and Visual Studio 2010.

I added an Event Receiver to a new Visual Studio 2010 project.  Very simple.  It was of type EmailReceived but I don’t think that matters in this case.  I went to deploy the project and got the following error message:

“Error occurred in deployment step ‘Activate Features’: Operation is not valid due to the current state of the object”

Apparently reading up on many people’s posts this can be many things.  Turns out mine was because I did something so normal:  I renamed the namespace and the class name of the class.  Well apparently when I did that, I got out of sync with the automatically generated Elements.xml – which I couldnt’ find at first.

So pop open your “EventReceiver1″ file in solution explorer – expand the files underneath it by pressing the + sign.  Double-click the Elements.xml file.  You will see something like this:

<?xml version="1.0" encoding="utf-8"?>

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
   <Receivers ListTemplateId="101">
      <Receiver>
         <Name>EventReceiver1EmailReceived</Name>
         <Type>EmailReceived</Type>
         <Assembly>$SharePoint.Project.AssemblyFullName$</Assembly>
         <Class>YourProjectNameHere.EventReceiver1.EventReceiver1</Class>
         <SequenceNumber>10000</SequenceNumber>
      </Receiver>
   </Receivers>
</Elements>

My problem was the <Class> element.  I had renamed my namespace to MyNamespace and my project to MyProjectName.  So my class should have been MyNamespace.MyProjectName.  That was it.

Easy