without a better message as to which file wasn't found, we can only guess. Possibilities are:
1) the path to your project does not conform to networking rules - no spaces, only latin letters, limited number of special signs only.
If you are not sure about this, give us the full filepath from c:\ to index.html and we can check for you.
2) you accidentally deployed your game into your working directory
If you are not sure if that is the case, open your working directory for the game and check if it has a folder named www.
If that is the case, come back here with the info and we tell you how to repair it.
3) your RMMV is 1.6.1 but your project is older.
please tell us your editor version (menu-help-about) and go to your project folder, open the rpg_core.js file with a text editor and read the version number in the title line (no number is 1.0)
Then post those two version numbers here.