This is just a "For Your Information", rather than being a bug or an issue ...
I am using WPDB-Optimizer (latest release) along with several other plugins on both a 'live' site, and a 'test' site housed off-line using "Desktop Server" software.
The plugin 'Admin Menu Editor' enables one to customise the dashboard menu - basically the options on the left hand side of the admin screen. One can 'move' items from a 'top level' position - i.e. so that they're there directly on the navigation bar, as WPDBO usually is - to the second level, or rename the menu item, etc.
If I move WPDBO to a second level position - in my case under the top level nav item 'Tools' - it stops working. Instead, I'm directed to a 'warning' notice informing me that I don't have sufficient privileges to access that page. If I leave WPDBO where it is, I can access it normally, whether or not the 'Admin Menu Editor' plugin is active.
So it isn't exactly a 'conflict' ... the WPDBO nav item just doesn't seem to like being moved. Not an issue really ... just letting you know. I haven't found any other plugins that don't like it (I use 30 - 40 offline) so thought I should mention it.
Best regards (and 'thanks' ... the optimizer plugin is one of those that when it works as it should you almost forget is there!)