Left with blank admin pages

I recently upgraded to 1.5 and am having some issues. Last night I installed the One-click plugin manager and once the plugin was activated, when I’d browse to its admin page, the page was completely blank. I wrote it off as a fluke and contacted the plugin author. This morning I installed spam karma manually and once I activated the plugin, my /wordpress/wp-admin/ page and all others under wp-admin are now rendering blank as well. Any ideas? It happens with Firefox and Safari.