Button in TinyMCE returns "page not found"

I was affected by this bug, too. There are actually two situations which make the bug appear. Here's how to reproduce.

1. Install a brand new Drupal instance.
2. Install code snippets module (with all of its dependencies) and enable its button for TinyMCE.
3. Go create a node (this should be the first node on this Drupal instance), click the code snippets button on TinyMCE toolbar - get a 404 page.

Now go create a node once again. This time do not touch the code snippets button on TinyMCE toolbar, just create a node with some random text. Then go and create another node - now click the code snippets button on TinyMCE toolbar - the window of code snippet insertion pops up. Insert some code and save the code snippet, then save the node.
Now go to administration section and delete all the nodes you have previously created. Then go create a new node and click the code snippets button on TinyMCE toolbar - get a 404 page. This time creating a node with some random text won't help. You're stuck with non-working code snippets module. The only way to fix this problem I've found so far is to reinstall Drupal from scratch.

Does anybody knows how to solve this problem ?

The steps described by #2 raises exactly the same error for me. Any idea, someone?

Although this bug can be systematically reproduced by following the exact steps described in comment #2, after some time, I noticed that it vanishes automatically by itself, without needing to reinstall Drupal from scratch.

I just reproduced it, did something else a few minutes, and when I came back to my test website, it was working again. The only thing I did was navigating around several administration pages of the website. I'm not sure why it disappeared, but it may be due to a cache.

If facing this issue, please try to clear your Drupal/browser caches and tell us if you still have the issue.

The remaining part of the problem is that we cannot use the code snippet button on a non-existing node (eg. the node has to be saved first without any snippets, and may then be edited with snippets).

This issue is fixed in the development version.