I've had happen fairly often with the Nexon launcher. You can use the Steam launcher instead ( I haven't had any major issues with it ). Or you can take the following steps and it will usually fix things, for a while.
Go to your games install folder. If you chose the default settings when installing that's going to be C:\Nexon\Library or press the little gear icon in the Launcher to bring up the game settings and click the "Open game location link"
Go the games folder
Rename the maplestory folder something else like maplestory1
Press Play on the launcher
The launcher should no longer see the game and begin to redownload the game. Press cancel, not pause.
Open the game settings in the launcher and click uninstall
If you kept the file explorer window open go back to it and change the name of the game install folder to something else like Games1
Now open the Nexon launcher settings by clicking the arrow next to your profile picture.
Scroll down to "Game installation location
Click on "Change Folder"
Select your newly renamed games folder. You will probably see an empty folder with the old name, this was created by the launcher, and you can delete it later.
Go back to the maplestory folder and rename it back to just maplestory
Press download on the Nexon launcher, it should verify that everything is in its proper place and switch to a "Play" button again
Press play and if everything worked all the pathways will have been reassociated in the launcher and allow your to play again.
I was going to make a new topic, but I guess this one fits the bill.
Currently players have 21 stages to complete in 5 minutes, meaning about 14 seconds to beat each stage. For a player that can one shot each map that's not a big deal. For everyone else its going to be a problem, especially if Mihile gets his damage reduction off or Ranmaru ends up seducing the player.
I think the timer should be bumped up to at least 10 minutes or back to the original 25; I don't see a good reason for it to be so low. As is, it's only punishing new players and characters.