Try saving the file directly to your Desktop or another local folder on your primary hard drive. If this works, the issue is with your network connection or the external drive’s permissions.
The most common culprit is Illustrator's "Background Save" feature. While it’s meant to let you keep working while a file saves, it often causes conflicts with cloud-synced folders (like Dropbox or OneDrive) or network drives. Try saving the file directly to your Desktop
If the error occurs on a specific file, try converting your text to outlines ( Shift + Cmd + O or Shift + Ctrl + O ). If it saves successfully after this, a specific font in your document is likely corrupted. While it’s meant to let you keep working
Sometimes Illustrator will fail an .ai save but succeed with a .pdf . Ensure "Preserve Illustrator Editing Capabilities" is checked. Sometimes Illustrator will fail an
The "Unknown Error" often relates to the video card not rendering a specific effect.
Sometimes the software's internal settings become "clogged" or corrupted. Resetting them is a standard "factory reset" for the app.