[GNC] Can't delete security

[rsbrux]

Because of the well-known difficulties associated with assigning the 
correct currency to a security, I need to delete and recreate a 
security.  I have deleted the initial transaction I created for this 
security, as well as the investment account I created for the 
transaction.  Nonetheless, when I try to "Remove" the security from the 
"Security Editor", I get the message:

"That commodity is currently used by at least one of your accounts. You 
may not delete it."

I am using GnuCash 2.6.19 running under Ubuntu Studio 18.04

How can I correct this?