I can run Addictive Drums as a stand alone plugin, but trying to use it within X3 causes X3 to crash. In fact AD will not even open as a plugin. It just whites out and closes down X3.
Anyone else experience this and fixed it?

My AD runs fine with X3. Try running your xln online installer. It can check for installation error and make correction accordingly. You do however need to have internet connection.

Try putting the Performance Module into the Control Bar and see if it's maxing out your CPU/RAM/HDD.
 
Right click on another module in Control Bar > Performance Module... the perf mod will replace the current module.
 
Can you give some more detailed system specs?

+1 to re-running the online installer.   There have been quite a few people posting about using AD in X3 over the last few weeks, myself included, that it's likely to be a one-off install type issue.    You could also try a Reset and Rescan first just to be sure that's not it.
 

Ran the XLN installer, but no difference.
 
Beepster, can you clarify the performance thingy
 
OS Name Microsoft Windows 7 Home Premium
Version 6.1.7601 Service Pack 1 Build 7601
System Manufacturer Intel
System Model DG41CN
System Type x64-based PC
Processor Pentium(R) Dual-Core  CPU      E5700  @ 3.00GHz, 3000 Mhz, 2 Core(s), 2 Logical Processor(s)
Installed Physical Memory (RAM) 4.00 GB
Total Physical Memory 4.00 GB
Available Physical Memory 2.83 GB
Total Virtual Memory 3.99 GB
Available Virtual Memory 2.83 GB