[Plugin: Custom Post Widget] Upload/Insert Button Doesn't show in Post Editor (Error)

Are you running a localized version of WordPress? It might be that there is a problem with the translation. This is the first time I hear of this issue, and therefore I think it is more likely caused by an external factor (another plugin or translation file for example) than by the plugin code itself.

Yeah, I’m running a localized version. I’m using MAMP on OS X. I did a test where I deactivated all other plugins and only activated the Custom Post Widget. The Warning only shows up when this plugin is activated. I disabled error_reporting in MAMP and the warning disappears, but the upload/insert button still doesn’t appear. Is the plugin not supported in English?

Yes, the plugin fully supports the English language. I think you meant to say that you are running a local version (MAMP). Localized means in this context that you are running a version in a language other than English. As I explained this is important because there could be an issue with a translation string. As you asked if English is supported I assume you are not running a localized version and therefore this is not an issue with a translation file.

As I have not received any other reports of any issues with this button and because your error message points to a core file (not to a file of the plugin) I think there might be some sort of issue with your install. Therefore I would suggest reinstalling WordPress or trying to replicate the issue on another install.

I have the same problem. My install of WP 3.4.2 is german. After Updating the Plugin, the “upload/insert” button was replaced by “add content block”. What can i do now?

@rezwiebel this is not the same problem, see my reply in the other support thread you posted to.