Updating document field value in SPItemEventReceiver.ItemCheckingIn() event handler

I need to update a property on ItemCheckingIn and came across this blog. Lucky me.

I have tried method 6
     properties.AfterProperties.ChangedProperties["Field Internal Name"] = "New Value";

but I couldn't get it working.

"Field Internal Name" should be "vti_Field Internal Name". Microsoft purchased SharePoint from a company called something with VTI. Unfortunately this didn't work either.

This blog is also worth reading as it explains the sequence of events.