This operation has been cancelled due to restrictions on this computer.

One day, and without warning, my version of Microsoft OneNote 2007 popped up with an error message

This operation has been cancelled due to restrictions on this computer. Please contact your system administrator.

This happened whenever I clicked on a hyperlink. Normally my Firefox web browser would launch, but I started getting this error instead. It also happened with Microsoft Word documents, but not with certain other programs.

After a huge amount of research, trial and error, and not wanting to re-install any software, the error was solved as follows.

Open the computer’s Registry Editor by clicking the Window key and start typing ‘Registry’.  Once Registry appears in the search dialog box, hitting Return will launch Registry Editor.

Back up your Registry just in case

^ [click to see] Back up the Registry by right-clicking Computer, Export...Taking a backup of the Registry is easy. At the top left of the Registry Editor pane is the ‘Computer’ icon. Right-click on it, and the ‘Export’ option appears. You can then backup your Registry by creating a file of any-name-you-like.reg and save it to disk. This may take some time.

Then click the Computer icon to expand the Registry ‘tree’. The path you want is Computer\HKEY_CLASSES_ROOT\

Scroll down the list of file types until you find .html    (You can also search, using CTRL+F)

^ [click to see] Ensure Default is htmlfile as shown

The default should be htmlfile [all one word] but mine initially showed Html.file [with a full stop] instead. I assumed this was left over from a Firefox bug, or, changing my default web browser at one point. It's what was causing some program hyperlinks to fail to launch the web browser properly.

Still in the Registry Editor, right click on Default, go Modify and change to htmlfile [all one word]. 

You might need to do this for .htm filetypes as well. Then reboot your PC, and try clicking links in OneNote again. It worked!

Comments welcome below.

• Also see Microsoft knowledgebase article https://support.microsoft.com/en-us/help/310049