I recently upgraded to 10.5.1 (from 10.3.1) and I am suddenly getting script errors when trying to run certain standard tools in the toolbox (e.g., Data Management - Calculate Field) in ArcMap or Catalog. It says there is an invalid pointer and provides a URL: file:///C:/Users/Amanda/AppData/Roaming/ESRI/Desktop10.5/ArcToolbox/Dlg/MdDlgContent.htm. I also am frequently getting the following Windows Security Warning when I try to open/use some tools: An ActiveX control on this page might be unsafe to interact with other parts of the page. Do you want to allow this interaction? It sometimes renders the tool unusable. Help!
download, unzip and follow the instructions for the file in this link....
This fix did not work for me on 10.5.1.7333 - so I upgraded to 10.6 and that resolved the ActiveX warning message.