If my Active Pokemon is Snorlax with the "Block" Ability, what happens to my opponent's Active Pokemon if I play Escape Rope?
Escape Rope causes the Pokemon to switch, but Block only prevents Retreating. The opponent switches their Active Pokemon when Escape Rope is played.
Source: Plasma Storm FAQ (2013-02-07), TPCi Rules Team (2013-02-07)

Relevant cards

Note: All applicable cards may not be listed below.
DP1_37
BW8_101