I have solved it on Win7 Pro 64bit
The only issue is that you need to "Run as Administrator" when you place the tick, and you can remove the "Run as Administrator" later
1. Go to XnView Icon
2. Right Click > Properties
3. Click [compatibility] tag
4. Tick "Run as Administrator" / You may need to test as "add to all users"
5. Click Apply & Close
6. Run XnView
7. Go to Tools > Options > System Integration
8. Tick (Add Browse with XnView to Context menu)
9. Click OK
If you are annoyed by the windows popup security message, remove the tick for "Run as Administrator",
the XnView System integration stays in the context menu.
This Worked for me.