[Garan]

It is odd that you only get the message 'Unable to load "ItemTreasury".'
Usually this is preceded by an error message. There are two common reasons this might not happen - there may be other reasons but you should check these two first.

First, you may be trying to load an already loaded plugin. When you list the plugins, there should be two lists, the first are "Available" plugins, the second list are "Loaded" plugins. Be sure the plugin is not in the "Loaded" plugins list, if it is, you might have to use the chat command "/item" to display it (I don't use Item Treasury, but it may simply be loading minimized)

Second, you may have the Error channel off in your channel filters. The 'Unable to load' message is in the Standard channel but Lua specific errors are in the Error channel. Right click on the tab of your active chat window and select 'Change Filters', then make sure the Error channel is selected and try loading the plugin again. You should be getting a more specific error message that tells you why the plugin does not load - if you paste that full error message here or in the download thread for the plugin the author or users that use that specific plugin should be able to provide further assistance.