problem installing plugins

I attempted to install role_manager or dchat plugins by first downloading plugin and moving the unzipped file to the plugin directory. Problem is when I go into Admin Panel to activate the plugin, it is not there.

Second plugin problem trying to install the Buddy Press Forum – Message Board I install using the Admin Panel but when I activate I receive a an error message (cannot find function). My first thought was now to go back into the Admin Panel and deactivate the plugin however this is not possible since whenever I attempt to enter the Admin Panel that is when the problem occurs. — I am able to execute the website as it was but I now have no Admin Panel.

I am finding that when the plugins install without any errors and I can activate them I seem to be successful. However when this kind of an impasse occurs I can only depend upon using a backup to get back to where I was. My alternative has been to continue to find another plug-in or in some cases I have been able to modify existing wordpress code.

If anybody has any suggestions it would be appreciated.