Kevin's answer is correct. The sure fire way to see opposing team rosters is to use League Roster and sort by team.

The reason it works in one league and not the other is that the leagues are in different phases. In most phases you can see the "player availablity" by clicking on the team's name in the standings. But in some phases of the game, namely any time after the end of one Sandbox season and the end of the following NFL season, the "player availability" data (which players are available during which games) is not available, so I don't allow those pages to be pulled up during times when the data is obviously wrong. I should probably provide a different screen that shows the roster without the player availability data that would be displayed when the player availability data wasn't up-to-date.