I am using Endnote X6 and encountering a strange problem.
I have a smartgroup with reference of 34. If I click on one reference that I intend to look at, endnote thinks for a while and then highlights another random reference. I think it happens when I click unread (bold) references.
How do I get rid of this? Is this a bug? Thanks 
The behavior you have described should not happen. It is most likely a problem with the preferences or the library.
As a test you can try the Sample library. When you click on File >Open > Open Library, you can go to C:\Program Files\EndNote X6 or C:\Program Files (X86)\EndNote X6, if you are on a 64-bit system. In the EndNote X6 folder you will see a shortcut to the Examples folder, and when you open the shortcut you can open the Sample library.
If the Sample library works normally when you click on a record, there is probably some corruption in your regular library. EndNote has a utility for repairing damaged libraries. It is called Recover Library, and you can find the command under the Tools menu in EndNote
If you experience the same behavior in the Sample library there is probably an issue with the EndNote preferences. Resetting the preferences would require using the Registry Editor to remove the key "HKEY_CURRENT_User\Software\ISI ResearchSoft\EndNote\Preferences.
The Windows System Registry is a critical part of your computer. If you are not familiar with using the Registry Editor you should either ask a friend to assist you or contact Technical Support.