There is a limit to how long a post can be for some people, especially the newbies to this forum/software. It can be fixed, however.
If you just use the reply box at the bottom a a thread, you get to typing along, and you might discover that after you have typed any fairly long page, the Blue Reply button has disappeared.
To fix this if it happens to you, you can then use Control-X for the last two-thirds of your post, this shrinks your reply box back down so the button shows, then you click on "Use rich formatting" and paste your 2/3 post back into place,,,,,,,,they you can continue typing and you will have the Reply button again when you finish.
You don't have to believe me, just type abc, Enter, abc, Enter a bunch of times and you will see the limit that the button disappears.
Rex