I get an internal security error when trying to block or permanently delete these emails with the red badge (icon).
Do you mean this icon?
This icon means the email has a valid digital Signature. (What do the Outlook icons mean?)
For Encrypted emails, try Shift+Delete and choose Yes.
Some ways are also mentioned in these similar threads:
Since you no longer have the certification to operate the encrypted message, the workaround is to drag these emails to a new PST file and then delete that PST file.