For our Forum Geeks.Fyi (https://www.geeks.fyi) we were using Ajax Upload Multiple Attachments Plugin version (1.4) for the MyBB. It had some issues when we try to insert the attachments to the Editor. After checking the JavaScript file found that it was using a method which will not work with the latest versions of CKE editors.
So if you want to use the Ajax Upload Multiple Attachments Plugin version, download the plug in, Unzip the files to directory
1. Open the jScripts folder and find a file named myproattach.js.
2. Open it in a text editor
3. Find and replace ann instances of $('#message').sceditor('instance').insertText with CKEDITOR.instances['message'].insertText
4. Save the changes
5. Upload the file (If you already using the plugin, replace the file inside the jscript folder).
Reload the page and try, it should work.
