Several days we released nopCommerce 3.30. It has an issue with TimyMCE editor. Relative URLs (e.g. in message templates, images in product descriptions, etc) were not properly handled (extra parts to URL were added). That's why we've just released a new version of nopCommerce. Unfortunately, picture uploading plugin to TimyMCE editor should be disabled now.
So if you downloaded nopCommerce 3.30 before April 12th, then download the latest version again here (its version is still 3.30). Or you can manually apply the fix:
Please see changeset 24cfd320b20c
or simply replace your existing \Administration\Views\Shared\EditorTemplates\RichEditor.cshtml file with the following new one - http://downloads.nopcommerce.com/RichEditor.rar (unpack first)
Thanks a lot to ReliableISS for reporting
Of course, you can enable picture uploading. Just open \Administration\Views\Shared\EditorTemplates\RichEditor.cshtml file file and remove the following line of code: "canUploadPictures = false;". But in this case you'll get issues when editing message templates. If you're not going to use this functionality (edit templates), then you can enable picture uploading