Server errors happen sometimes - more often if you are using the app. This can happen because someone is editing a post you are responding to at the moment you are posting, they deleted the post in question or you used a forbidden word (although they usually tell you that you used a forbidden word, they just don't tell you what that word is so you have to guess), or simply due to a wonky connection or too much site traffic at the same time. You just have to try again. I have gotten into the habit of copying my text to the clipboard just prior to hitting the "post" button in case this happens. This way, I don't have to type everything all over again if this happens. You can also pre-write your post in a notes app and copy and paste into the entry field.
