This is due to a missing or incorrectly installed Microsoft sofware module. The potential solutions are described in Text Editor - Word Processor error - Unable to Load/Create Dialog Item of type "HTML". Options 2 or 3 are the most likely candidates.
Also if the DHTML Editing Component is already listed in the Programs & Features Control Panel, right-clicking and picking repair may resolve the problem. Close Internet Explorer and AECOsim before running the repair.