After installing a cloud storage server client, like Dropbox, it can happen when double clicking on the client icon in the taskbar, that the media-player Vlc opens instead of a file manager. This is caused by a wrong entry in a file called mimeapps.list. To solve this issue, some editing must de done in this file.
Here's how to solve this problem with Vlc opening instead of a file manager:
Open a file manager
Press Ctrl+H to show hidden files and folders
Go to: /home/{username}/.local/share/applications (take notice of the dot in front of the folder name)
Right click on the file mimeapps.list and select Open with text editor
Search for the lines starting with: inode/directory=
Check if this entry is given: vlc.desktop;
Change the entry into:
For Mate-based distro's: caja.desktop;
For Cinnamon-based distro's: nemo.desktop;
Save and close the file.
The problem should be solved now!