If you don't tell the creator enough information, they can't fix it. Send a message to the creator of the addon, along with the specific error which can be found in the console and what you were doing that caused the crash.
You should ask the developer to fix it, rather than Garry. If so, then it's likely that either the addon is from Garry's Mod 12, or the developer made a mistake. If you just installed an addondisable it and see if that stops the crashing.
