If none of these steps work, visit the Adobe Community forums and share the exact action you were performing—along with your OS and Illustrator version. Often, the specific context holds the key to a final fix.
If you’ve been working in Adobe Illustrator and suddenly been confronted with a cryptic alert box reading simply "Parm Error," you know the unique frustration it brings. Unlike a standard crash or a "not responding" message, the Parm Error is vague, technical, and can halt your workflow instantly. parm error illustrator