I have these macros that are words made out of "#"s... For some reason they won't work in guild chat anymore, but I can send them through whispers or in party chat. My friend is having the same problem.

Here is an example:

# # ### # ### ### # # ###
# # # # # # # # ## ## #
# # # # ### # # # # # ## # ###
## ## # # # # # # # # #
# # ### ### ### ### # # # ###

Err, supposed to be "WELCOME"...

Anyway, it only shows the first line.

This was an anti-spam measure, and will shortly be allowed in guild chat and private channels with 25 people or less.

This throttling is now currently active only in chat channels with more than 25 users, and not in party, raid, or guild chat

The recommended way for AddOns to communicate is using SendAddonMessage():
http://www.wowwiki.com/API_SendAddonMessage