Sometimes things get out of sync. Right click the folder and select Mark Folder Read to clear the number.

Mark Folder Read did not remove the unread inbox bold noice

Right click the folder and select properties. Then Repair Folder.

Then read this article about folder maintenance. http://kb.mozillazine.org/Keep_it_working_(Thunderbird)

Tried all this and still cannot clear the bold Inbox(1) message.

Do you have 'View' > 'Folders' > 'All' selected?

i have heard of some reports saying that the 'Unified' view can show incorrect number.

Do you have any add ons installed? If so, go to the Help menu and select Restart with Add Ons Disabled and then close and restart Thunderbird.

nothing so far has fixed the problem

Right click the folder, select properties and then the repair button. A new index might clear it.

If not try View menu > folders > unread see if Thunderbird can find it since it says it is there after an index rebuild.