Jonny

I'm not an expert at troubleshooting these sorts of things, and I haven't looked specifically at your error, but I would look at trying the following:

1. Download a fresh copy of Screen Monkey 3.6 from the website. There's a possible chance it corrupted during download.
2. Delete the Screen Monkey folder inside Program Files (if it's there) before starting the install.
3. Make sure you are an Administrator user on the desktop. Running it as a limited or regular user will cause permission problems that may cause it to not read/write files properly during install.
4. Disable all antivirus/antispyware software while running the install. I would suggest that you are not online when you do that. Normally Screen Monkey does not have problems regarding this, but it's a general principle when installing software.

Let us know how things go and we'll troubleshoot from there.Thanks

It is possible to install the software by copying the install folder. The only problem you will find is that plugins may not install correctly and will just say that SM is not installed. 

Once you have copied all the files and applied the nesasery permissions you will need to run GMFBridgeSetup.exe and XulRunnerSetup.exe manually.

I have recently run into trouble with another system and corrupted .net frameworks (completely unrelated to your issue), but I think this tool I used there might help you as well:

http://blogs.msdn.com/b/astebner/arch...

On that site is a tool for download that manually uninstalls .net frameworks.  I would suggest you go through the process of uninstalling all your .net frameworks on the system (starting from highest version to lowest), and then use the tool mentioned on this link to clean out any leftover entries from .net frameworks.

From that point, reinstall all the .net frameworks, and then restart the system and give the Screen Monkey install another try.  Screen Monkey completely relies on the .net frameworks working properly, so if there's a problem there, it must be solved first.