Just to be sure, when you're in-game, and you load your character, make sure it's saying "GuildRaidSnapShot Version 2.002". If it's saying 0.994, then that version blocks whispers.
The reason is to make sure that the mod is installed properly.
If that still doesn't fix it. Try disabling the GRSS mod altogether and see if that fixes it. If that doesn't fix it, then there's another mod causing the problem (apparently, it was a pretty common problem with many mods, not just the GRSS).
Interesting. I don't know what's causing it, since whispers are working for me.
This might be a big favor, but could you zip up and upload your entire Addons folder so I can try to test with your configuration and see if there's some sort of conflict with another mod? I'm at a loss at this point. I run vanilla WoW and it's working for me.
Here's a test, if you disable all other mods except GRSS, does it work then?