Some Items Can't be Deleted in Library Manager

[Anonymous]

For some items in library manager, I can't delete them. The red cross is grayed out.

How can I proceed to remove the duplicates, then?

[Barry Kelly]

Is it because it is a teamwork file and you don't have the permission to do this?

Barry.

[Anonymous]

No, because I've created the teamwork project.

[Laszlo Nagy]

I think the reason you cannot delete it is because it is within an LCF (Library Container File), as far as I can see from the screenshot.
The LCF file is a single file so obviously nothing within it can be deleted individually in the Library Manager.
You would have to extract the LCF file to a folder, then add that folder as a Linked Library, and then you could delete the individual items within that library.