MicroBlaze Simulation Question

Hallo! I'm only starting with Xilinx EDK, so i'm sorry for my probably
stupid question. Also my english is not a perfect.
The problem is: I use Xilinx EDK 10.1 and ModelSim SE 6.3d. I made a simple
project (led blink) with Microblaze and try to do behavioral simulation
from EDK (I have compiled sim libraries, generate simulation files and run
ModelSim). But when I run the simulation in Modelsim i see, that many
signals are in 'U' or 'X' state and the project didn't work in a right way
at all. Then I tried to do a structural model simulation and i was wondered
that it worked perfect!  For structural model simulation i did all the same
things as for behavioral (and of course i didn't change anything in my
hardware or software).
Tell me, please, what I have done wrong? I can't understand why I can't do
a behavioral simulation, but structural simulation work in a right way?
Thank you for attention, I really need your help.

	   
					
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