I like the challenges that limit the towers you can use, but don't like the ones that limit upgrades (without telling you, until you buy the tower. -.-)
Today's challenge.... Left towers can only use upgrades similar to the right towers. Am I the only one that is having trouble understanding what that means? O.o
You likely need to clear your cache and reload the game, if you can't see new tracks. I can't say for sure if that will clear your saved game or not, however.
Often, if you don't see the new tracks in your game, you need to clear your cache and reload the game. Unfortunately, I can't tell you for sure if that clears your save too or not...
 "Takeover"){kind=icon}
 "Bloons TD 5"){kind=icon}
 "Zombies In Your Backyard"){kind=icon}
 "Epic War Saga"){kind=icon}
 "Kingdom Rush"){kind=icon}