Sometimes there are hidden files left in the folder that were created by the program used by the file/folder (think of it as a index or directory of that folder of what was in there before you deleted it. For "record keeping" purposes, sometimes these are kept in the file, hidden, and if you don't have hidden files showing (can be done via Terminal) then it seems like the folder is empty when it's not). Few different options, which for all I recommend temporarily moving the files from the Trash to your Desktop if possible:
- You could check for hidden files in the folders:
- Open Terminal, run the following command: defaults write com.apple.finder AppleShowAllFiles YES
- After running the command, Right-click the Finder icon in your Dock while holding down the Option key and choose "Relaunch" to relaunch Finder with the new configuration. Check the folders for hidden files, and if you find any you need to unlock, follow the unlocking steps in option #2 below.
- To re-hide files, run the following command and don't forget to Relaunch Finder: defaults write com.apple.finder AppleShowAllFiles NO
- The folders may be locked themselves: Right-click>Get Info. Make sure that the checkbox next to "Locked" is unchecked and try deleting them again. You may need to click on the lock in the bottom right hand corner of the "Get Info" window and input your Admin credentials to get elevated access to modify options.
- You could try holding the Option key as you choose Empty Trash from the Finder menu. - https://support.apple.com/en-us/HT201583
- There are apps you can try as suggested by PATRICKMELE, but honestly I'm not a fan of adding apps to solve infrequent issues like this. You can always try the following commands in Terminal:
- chflags nouchg Path_To_Folder_Here (You can drag and drop the folder into the Terminal command after nouchg to auto-populate the path). This will unlock the folder if it is locked.
- chflags nouchg Path_To_Folder_Here/* This command, with the /* trailing at the end, will recursively unlock any folders/files within the parent folder.
- If all else fails, there's always the good 'ol sudo rm -rf command which takes superuser leverage and (usually) kills the folders/files without issue. Use the command as follows:
- sudo rm -rf Path_To_Folder/File_Here (again, you can drag and drop the folder into the Terminal command after -rf to auto-populate the path)