Missing Invoice

[Roman]

I run GnuCash 2.4.13 under Windows 7-x64 using MySQL as the database
backend. I created an Invoice having an Invoice ID 'ID01', and posted it
into an account (receivable). I now want to remove that posted entry and
replace it with a different modified Invoice. In order to do so I must
unpost the Invoice which will remove the entry.

However, on running the 'Find Invoice' script, I get a list of ALL my known
invoices except 'ID01'. And on checking the MySQL database 'invoices' table
I see that this invoice is not present! Thus, I cannot remove that entry.
But the entry for this transaction (posting the invoice) can be found in the
'transactions' table. (By the way, that invoice did exist until recently.)

How should I proceed? Based on developer recommendations, I have made no
modifications or deletions directly via MySQL. Furthermore, there apparently
is no intent to provide Invoice removal options. Is it safe to remove the
record in table 'transactions' referencing Invoice 'ID01'? Or can I add a
record to the 'invoices' table with the proper guid? Where would I find that
guid?

Is there a set of actions that I can perform on the MySQL backend to remove
this unwanted invoice transaction for a missing invoice?

Thanks for any help here.

Roman