Lag Valley refers to the Imperious Task Force on the third mission, Stop Romulus, specifically the valley where the second general is fought. Upon engaging in combat with him, a large ambush of Cimeroran Traitors is spawned, which would immediately cause a huge duration of repeated lag of powers and possible mapserve for all players, regardless of their computer performance and graphic cards. Players would frequently see the "lost connection due to mapserve" message. Area of Effect powers, Point Blank Area of Effect powers, and more ambushes by the Cimeroran Traitors would increase the frequency of the mapserves. The lagging duration would end upon leaving the valley (such as nearing the 5th Column area).
The term Lag Valley appeared to only exist on the European servers Union, Defiant, Vigilance, and Zukunft, due to the lower grade servers based in Germany.
With the migration of the four European servers to a new data center in the United States on November 11, 2010, with newer, more efficient hardware, performance improvements in the Imperious Task Force resulted in the Lag Valley's name becoming mostly obsolete.