Cannot Move in-game
From Intense Ragnarok Online Wiki
Character Stuck or Cannot Move in-game
Just press ALT+TAB and go back into the game. You should be able to move after tabbing back in, unless you were previously sitting and clicked on the Heal & Buff NPC which you'll have to press Insert (Sit) then try to stand up again.
- Some players have reported that this is not just a little issue for players who play in Windowed Mode; even in Fullscreen you can get this.