did you at all move the info_landmark at anytime even a billionth of a centrementre? Because if you did I think that could screw things up. The landmark must be in the exact same place for both maps. Example:
there is map. it's called Map1.
Map 1 has a info_landmark and a trigger_changelevel. It also has a player_start entity. Snpbond wants to go to another map. So, do THIS EXACTLY. He goes file > save as and names it map 2. Now, he goes and open Map1 again keeping Map2 open. He now has two maps exactly the same. He selects the info landmark in map 1 and changes the properties.
Name : landmark1
He then closes it and then selects the trigger_changelevel and goes to it's properties:
Name: Leave it blank
New Map Name: Map2
Landmark Name: landmark1
he then closes it, saves it and opens up map2 again. He goes into the properties of the info_landmark and gives it the name of landmark1.
He then opens the properties of the trigger_changelevel and changes the settings to this:
Name: Leave blank
New Map Name: Map1
Landmark Name: landmark1
He saves them both. He compiles them both but ticks "don't run the game after compiling" for both of them. He then goes into Halflife2, goes into the console and types this in: map map1
Map1 runs, he goes into the trigger_changelevel and he then ends up in map2.
Map2 does not need the player_start but no harm done if you keep it there.
END.