I am using XOOPS 2.0.18 and smartsection 2.13 and i have made no upgrades or changes.
Does anyone has an idea how this comes?
Which xoopseditor are you using?
Smartsection 2.13 doesn't use xoopseditors in the class/xoopseditor folder. Rather, it looks for editors in a folder class/wysiwyg. See this article on Mark Boyden's website. I got Koivi working this way.
If you haven't changed anything or deleted any editors then you need to be looking at something else. Have you tried clearing your website's cache? Also, try going into preferences and checking for template changes.
Has your hosting company changed anything? Check for permissions on the cache and template_c folders (which should be writeable).
Smartsection 2.13 works fine on XOOPS 2.4.3; any reason why you haven't upgraded yet?