So first thing you're doing wrong : your file host ^^
Really, prefer using dropbox, so that the users don't have 5 click and a captcha to answer, this is just bad.
Then, you should use instances rather than showing/hiding your gui elements as you go by.
For now you have three, but I bet you're aiming for "a big game" and you'll end up drown in thousands of such objects.
Rather than Next, Next1, Next2, etc... use a single object and private instances to see where you're at.
There are several dialog systems in the how do I FAQ
dialog system with answers - LINK
Visual Novel/Dialogues example - LINK
I strongly suggest to check them out and find a way to implement/adapt them in your own game.
It's not an easy task, but dialogs are a complex subject.
Good luck <img src="smileys/smiley1.gif" border="0" align="middle">
Edit: also I forgot, the current problem is because when you use the condition "click on Next" the click occurs when the mouse button is down.
This makes the second sentence appear, but as you're still "clicking" for C2, it jumps to the third, and the next one...
Checking the examples will allow you to wait for the user's action before displaying one sentence or another.