Why are some players on my roster labeled as Can't Drop?

Most leagues will lock recently added players. Owners can gain an unfair advantage by adding and immediately dropping players, preventing other owners from acquiring them until the following week. By default, Fleaflicker will lock recently-added players within 24 or 48 hours of the start of their game (depending on your league settings) to ensure this does not happen. To disable this setting, go to League » Settings » Edit Waiver Wire Rules » Lock Recently Added » No.

Note: This setting depends on your league's configured Time on Waivers After Drop.