>>You didn't day whether the assembly will have access to the internet.
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>We can mandatory that. So, yes, it could be.

If there's an internet connection you could roll your own. Could be easy to implement using SignalR - each usage to keep a 'heart-beat' with the server which would then only allow xxx connections at any one time. Of course that would mean that the assembly could be installed on more machines than were allowed - but if the total number in use at any one time is controlled then that may be a good thing ?

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>>But, more importantly, if they are able to view the code then what's to stop them modifying it (or just duplicating the functionality)?
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>If modified, upcoming upgrades will collapse on top of that. Unless, they subclass. But, most importantly, the goal would be to assure, or try to achieve some of that, that if a licence is sold for 10 PCs, then, the project cannot be used on the 11th PC.
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>>One of the options here: http://www.eziriz.com/ might be suitable (which one suits best will depend on your needs)
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>Thanks, I will check that out.