When the address is valid an ALE signal is asserted, so the target system logic can latch it. Some power will flow between the emulator and target, even if only in the signal lines. If the target's power distribution tracks on the PC board are poorly designed, then the emulator can induce even more noise. You would be amazed by the number of systems we see with miserable power and ground tracks. A few weeks ago we received one with power tracks only .012 inch wide.
Wide tracks are important to reduce switching noise.
We recommend 4 layer boards for most new designs. Be sure your design has plenty of noise margin, as the emulator will only make the problem worse. Consider noise at each step of the design. The single biggest hardware problem we see is noisy or inadequate clock circuits. Microprocessors are very sensitive to the clock's voltage level, duty cycle, and noise.