Validation on lead conversion's 'ISNEW' field

Question

trying to create a validation rule to NOT let disqualified leads be converted WITH a new opportunity. Just attach into the existing account/contact.

I managed to research the validation rule components and it's around the ISNEW() field. Can you please review my code and help me find the error? It still lets users convert leads with new opps.

AND 
( 
ISNEW(), 
ISPICKVAL(Status, "Unqualified") 
)

Just to elaborate, it's this checkbox on the lead page that i'm talking about:

Answer 1

Try this:

1. Create a Checkbox field lets say 'IsNotQualified' on Lead object and set the default value to False.
2. Create another checkbox field lets say 'IsLeadNotQualified' on Opportunity Object and set the value to False.
3. Map Custom Field IsQualified with IsLeadQualified.
4. Create a WF Rule on Lead Object with Evaluation Criteria as 'when a record is created, and every time it's edited'.
5. In WF Rule Criteria,Specify Lead status='Not Qualified' and add field update action and set 'IsNotQualified' value to True and Activate WF Rule.

6. Create A Validation Rule On Opportunity not on Lead Object:

   AND ( ISNEW(), lightingintro__IsLeadQualified__c = TRUE )

Instead of WF Rule You can also write a trigger on Before Insert of Lead and set the checkbox value to true.

Follow the steps and let me know if it helps.