Issue with connecting to games in Warcraft 3

This is an issue that arose for me awhile back and continues to happen. I have reinstalled windows since then so I doubt it has anything to do with my warcraft 3 installation

Here's what happens. Earlier today, I joined my buddy's game of Metastasis. After a few games, I was unable to join further games that he hosted. His game name would not show up in the list of games available. However, this is the interesting part. I type his game name in and hit join. The screen goes grey, but the name of his game INSTANTLY appears at the top of the list of available games and it gives me the normal grey screen error message(something along the lines of the game could not be found, are you sure you spelled it correctly?).

I'm able to join any other game that random people host and everybody else is able to join my buddy's games

I'm thinking it may be something to do with my router(D-link WBR-2310) or modem(Speedstream 5200) because this does not happen when I try to do the same from other computers

Has anybody else experienced or heard of this before? Any sort of tests I could do to try and determine/solve the problem?