Load the assembly without any componets first and then fully load one at a time to find the part causing the problem. Once you have found the part that is causing the problem then load that part first next time and delete the mating constraint that is causing the problem. Load the rest of the assembly.
NX6.0.4.3 mp02, Windows XP 32-bit
Running cad straight out of the box is OK but, a system tuned with application software is the best way to increase productivity.