I was recently migrating an old blog to community server through the web services API. For some reasons while migrating over the posts, it would die after the 36th item every time while giving a generic "The post could not be added" error. I thought that it could be something to do with that specific post, so I removed it from the list to migrate. Same error. So I began to wonder if it was some spam post count limiter, and there was no blog posting limiter. Needless to say, I was pretty confused.
I Google'd around, and eventually found this (http://communityserver.org/forums/p/491235/595600.aspx#595600) talking about Windows Live Writer and a similar error. The error occurs when there is already a post containing the same title. Since both the 37th and the 38th (the two ones it was dying on) contained title's that had already occurred in the migration process it wasn't apparent to me immediately this was this issue.
Anyhow, just a quick FYI for anyone who hits this issue.