A quicky page for a WildStar addon I created to combat this message, experienced by roleplayers and general long-winded people:
"Error: Your message to "Some Chat Channel" was sent, but was truncated to fit."
Details are on the Curse page, so I'm not going to keep this post updated. The file, however, will always be the latest one in case Curse goes down.
Current version 0.931 Uploaded: Oct 4th DL below. Change log at the bottom. More Details at Curse. Curse Page