Hi Steve,
it seems your system is not set up to derive the bank key from the IBAN - or maybe it's not possible for Canada at all. But it tries to do it, once you cpature an IBAN.
In that case the field BNKEY in table T005 should be set to '4', so the system knows it is not supposed to even try it and then clear it, because it can't. (In the normal config view for T005, this field is towards the top of the screen). This is normal procedure for soem countries and also used by many customers, who manually capture bank master data and don't use the SAP standard conventions.
If it is set on 4 and still doesn't work, please check, whether note 1869180 is applied in your system.
hope this will do the trick. Did it for quite a few customers in Luxembourg and various non-SEPA countries.
cheers
Sven