What is the cause if this?

[420benz]

This is the second time this happened on my new Desktop Mac

 

[tstafford]

I believe it means the target file (or application) for those icons has been deleted. So the icon no longer points to anything.

 

[wilberforce]

These are shortcuts to folders that you have somewhere else in your system, but you deleted them (or possibly moved or renamed them) such that the shortcuts can no longer find those folders.

 

[Fishrrman]

Remove those folders from the dock.
Locate the folders that are SUPPOSED to be there, and "re-drag" them back into the dock.

 

[420benz]

Remove those folders from the dock.
Locate the folders that are SUPPOSED to be there, and "re-drag" them back into the dock.

Where should I look?

 

[Fishrrman]

"Where should I look?"

No one here can tell you that, because we don't know what the folders were or where they came from.

What were they?

 

[DeltaMac]

Your system doesn't drag folders into the dock, and the folders don't appear in the dock, unless you dragged them there. Are you saying that you don't have any idea what folders you put there?
Does any folder name appear when you mouse across those folders (even if the folder won't open, it may show the name of the folder.
If you have an exernal drive, then drag a folder from that drive into the dock -- then eject that drive, the folder remains, but can't open when the external drive is not mounted. Any possibilities there?

 

[420benz]

The folders were named. One folder had a list of shopping stores the other had a list of forums. I reinstalled them. It’s ok now.Thanks for your help.

 

[AZhappyjack]

I see that on my Google Drive folders that I have in the dock... it only happens on a reboot... but if I click on one of the folders with the question mark, it properly resolves.