Folder not opening in DOpus

I have been a registered user of Directory Opus for some years and generally find it excellent. I have one query however. On a couple of occasions I have created a folder on the desktop, dragged some items into it and then double clicked it to open it. It opens OK, but in Windows File Explorer, NOT DOpus. I have DOpus Explorer Replacement set to "Replace Explorer for all file system folders" I am running DOpus 12.29 64 bit version on Windows 11. Any ideas?

Explorer Replacement won't work if Opus has been launched elevated (Administrator), which may explain why you see the problem sometimes but not others.

If the process is elevated it should say "ADMINISTRATOR:" in all caps in the window title. Avoid that, and instead use the Admin Mode / UAC support built into Opus (which will put "Administrator:" in the title instead.) See Why NOT to run Opus as Administrator under UAC for more detail.

Other than that, I don't know of a reason why double-clicks on the same folder, from the same program (e.g. the Windows desktop) would work sometimes but not others, unless the machine was under really heavy load and the Explorer Replacement check was timing out.

You said you have it set to set to "Replace Explorer for all file system folders". There is another option to "Replace Explorer for all folders".
I suspect that 'File system' folders means 'system' (C Drive) folders, but I'm not sure. Have you tried using the "Replace Explorer for all folders" option?

Thanks for the suggestions. I can confirm that I am not running Opus in elevated mode and there is no abnormal load on the machine. It has happened to me twice - both in identical circumstances - create a new folder on the desktop, drag some items into it, and then double click to open. If I navigate to the folder within Opus all works as you would expect. Haven't tried the Replace Explorer for all folders yet - but will.

Have tried Replace Explorer for all folders - still the same. It would appear that if I create a folder on the desktop and double click it, it opens in Windows File Explorer no matter what I do. It is a minor think, since I can navigate to the folder from within Opus and all works as it should, but it is frustrating.