You should pass an instance id (which you should have stored somewhere since you created an IM_NONE instance) to instance_enter command to let the server know which instance it should warp the player to. See script_commands.txt for more info.
Like Secrets saied, you have to set an variable for the instance you want to send the player to, also I believe that in instance_enter you will have to warp the player extra, since no one is attached.
The variable has to contain the exact same name as in the instance_db.txt.
If you need an example how instances work you could check the doc/sample/instancing.txt or look at the existing ones.
Regards,
Chris
illust's for a system of daily rewards, created by me, based on the official theme of ragnarok online.
It works with the script [rathena]: Daily_Reward_System
PS: If you like it, and give me reputation, it's important to me and encourages me to continue with my work!
best regards, ZelosAvalon