Welcome to the community. 
This is a common installation issue that is caused by interference from a security program on your computer or network, especially when you say update.exe is missing - only security or “clean-up” programs can generally delete files from your PC (unless you have a malicious virus).
Your antivirus can still have part of the software trapped in its quarantine chest, even when disabled.
Please see here for full troubleshooting: I can’t Install WeMod / “There was a error installing the application” - WeMod App / Support.