I just found this great blog article on how to get your Closed Activities Nav Bar item back. Check it out: http://social.technet.microsoft.com/wiki/contents/articles/4808.aspx

In the article, the entity that they are working with is the Case Entity. In my situation, I needed to get the Closed Activities item back on my Account Entity. Here is how I did it:

1. 1. I created a new solution in my problem organization called AccountTest and I put just the account entity into it. I then exported the solution to AccountTest.zip.
2. I repeated this process from another CRM organization that still had the Closed Activities Nav Bar on the Account Entity. This solution was called AccountOriginal. I exported it to AccountOriginal.zip.
3. I extracted the customization.xml file from AccountOriginal.zip, opened it and searched for the following xml tag: <NavBarByRelationshipItem
4. I was able to quickly find the xml section dealing with Closed Activities. I copied it to a notepad and closed the xml file.
5. I extracted the customization.xml file from AccountTest.zip and searched for the same xml tag as above. I pasted the xml snippet into this xml file. Then saved the xml file, deleted the original from the AccountOriginal.zip and then copied the new customization.xml file into the zip.
6. I imported the AccountOriginal.zip back to my problem organization. And just like that, Closed Activities was BACK! Easy Pleasey.

This was so much simpler than I thought it would be. Thanks for the great article, TechNet!

Here is the xml snippet that I need for the Account Entity:

<NavBarByRelationshipItem RelationshipName=”Account_ActivityPointers” TitleResourceId=”Tab_Label_History” Icon=”/_imgs/ico_18_history.gif” ViewId=”21E2B905-6FDB-470d-8517-AD69B4C01268″ Sequence=”20″ Area=”Info”>

   <Privileges>

      <Privilege Entity=”” Privilege=”ReadActivity” />

   </Privileges>

   <Titles>

      <Title LCID=”1033″ Text=”Closed Activities” />

   </Titles>

</NavBarByRelationshipItem>