Today, in all my drives in Windows 7 appeared a red icon. I try to delete the IconCache.db but doesn't work.
Update: it's caused by a change in the Windows system by the updates in combination with Dropbox. The Dropbox icon from folders is used on all devices. To fix it whithout deinstalling Dropbox I just removed the overlay icons (which I never bothered about):
Use the RegEdit to go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers
You will see a couple of " DropboxExt0x" entries (01-10 for me). You can export a Backup from the whole "ShellIconOverlayIdentifiers" entry and then delete the Dropbox ones. After a restart the issue is fixed (for now).
This is an issue if you are using the latest DropBox version. People fixed this by downgrading it.