I found this response from the maker of “Tweet This” (Richard X. Thripp) describing why this error (the 404 error) may appear here:
http://richardxthripp.thripp.com/tweet-this/#comment-87745
The 404 error Richard says:
“That usually means the tweet was over 140 characters or you published an identical tweet to Twitter in the past 25 hours. Also, make sure the Twitter application is set to “Read & Write” access.”
The commenter atif said that everything was in order but he still got the error; however, when atif checked out Twitter he found that the tweet appeared in Twitter anyhow even with the error in the blog.
After reading this I checked out my Twitter after posting from one of my blogs and getting this error. I too found out to my surprise that the tweet made it to Twitter even with the error in my blog.
So, I have to recommend checking this out for your own blogs to see if your tweets are making it to Twitter anyhow even in spite of the errors in your blogs.
Also, make sure to read the original response following the link above to hear it from the maker of “Tweet This” himself Richard X. Thripp.
If you still have any questions taking them to the maker of the plugin may prove to be more fruitful anyhow as here.
John