Hiya, I did try to search the closed issues for this exact error message but I couldn't find it. I'm not very familiar with github because I'm not that much of a code person but since the workshop page doesn't have discussions I figured I had to create an issue here to try troubleshooting opening this file.
Essentially this dupe has worked perfectly fine for a while and I haven't made any changes to my subscribed addons, for example or installed games that could have caused an asset to go missing and I'm not sure this error message indicates that either. The only change I can think of is the dupe might use HL episode content and they did roll the episodes into the HL2 executable but I don't see how that could be an issue, either?
From console:
[AdvDupe2Notify] Pasting...
[AdvDupe2Notify] lua/advdupe2/sv_clipboard.lua:1419: attempt to index a nil value
[AdvDupe2Notify] Finished Pasting!
In game it seems to paste the entire dupe no problem but the split second that the pasting progress bar finishes, the entire dupe disappears with no trace, and it notifies about the sv_clipboard thing.
The dupe in question:
4th dimension construct v3.txt