A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
That code should be working. I made a userform and it displays fine with this code:
Sub test()
UserForm1.Show vbModeless
End Sub
Assuming VBA is up to date (version 14.3.9) in the About PowerPoint while in the Visual Basic Editor, all I can suggest is look around for a syntax error nearby. The error message talks about a failure to create an embedded object. Do you have code that attempts to make an embedded object in this project?
You can sometimes fix a corrupt module or userform by using File > Export to save the module as a .bas file. Then delete the module or userform from the project. Use File > Import to bring the module or userform back into the project.