[Jennifer2010]

Problem resolved:
We have a custom "Upload Images" button that calls the same function as the insert image button does on the post editor. However, after we upgraded to 4.2.2 it must not be compatible. Thus, all we have to do now is find the new code and it should work (default vb style works perfect)

I can't remember where I found the old code:
<span class="cke_button">
<input type="button" style="height: 30px; width: 100px; font-size: 14px; margin-top: 15px;" a id="cke_38" class="cke_off cke_button_vbimage" onclick="CKEDITOR.tools.callFunction(77, this); return false;" onfocus="return CKEDITOR.tools.callFunction(76, event);" onkeydown="return CKEDITOR.tools.callFunction(75, event);" onblur="this.style.cssText = this.style.cssText;" aria-labelledby="cke_38_label" hidefocus="true" tabindex="-1" value="Upload Images">
</a>
</span>

Anyway it's not a server issue anymore, lol.