The 64bit version of Logic 9 is (as you probably know) brand new and might be unstable. I managed to get Addictive Drums 1.5.1 up and running in L9 64bit, but I had start the 32bit version of Logic first and do a "Reset & Rescan" on Addictive Drums in the AU Manager (Logic Pro menu -> Preferences -> Audio Units manager). After that I was able to load Addictive Drums in the 64bit version as well. Could you try that?
The same thing happens to me - AD will only work on an administrator account. However, it's not Logic that's the problem - it's every single DAW on my system - Cubase, Live, GarageBand, Tracktion, Studio One. This must be a deeper issue. What's the workaround? I'd rather not have to login to my admin account whenever I want to make music