Plugins’ buttons in Visual Editor doesn’t work

Hi, I hope you can help me with this (it was mistakenly posted in other sub-forum).

I’m currently using two plugins that insert buttons on the Visual Editor, within Post/Page write interfaces: NextGen Gallery and CForms. When you click either, a lightbox popup window (or thickbox or modal, however it’s called) should appear on top of the page, the same way that the image uploader does.

However, none of them load the plugin’s setting page, or anything, but an error page from my site.

I figure this must be a server’s error, probably due to the fact my site is running as a subdomain. Maybe I should look at the code each button executes to open that popup and call the appropiate URL, but I don’t quite know where to look.

Here’s a screenshot of the error I get.

https://diseno.udd.cl/?attachment_id=1092