Unless I am mistaken, you will discover that your client has restricted the RE account to accept specific currencies, and they have added a new one to their chart without adding it as an accepptable currency to be posted to the RE account.
Hence the requirement to permit all (source) currencies be posted to the Retained Earnings account.
I'm prepared to be proven wrong.
The restriction on RE account to, say, only CAD and USD, still doesn't explain the appearance of that error in the database, having only these two currencies.