Could be a few things
1)Mess up on first ICB report excluded some dodgy information on an outstanding loan
2)Bank check is picking up dodgy information from ICB. This has happened in the past(you only need to check some of the case studies at
www.dataprotection.ie to see examples).
3)One of you is not been totally honest about whats on their report-or misreading the report they have.At the end of the day it could be a number or letter on a payment profile that is incorrect/misinterpreted.
What I would do
1)Recheck the ICB reports you received and ensure that the payment profiles are fine. All 0's preferably and check that any letters that exist on it are not negative ones.
2)Have you any C/cards with the bank in question? If these are high or badly maintained then these may not be on the ICB system but certainly visible to the staff making the decision on the loan.
3)Reapply to the ICB providing all addresses that you would have had, perhaps you used a work address for a loan(I know I did at one stage).
Nobody can tell you that you have a good rating from an ICB report. The banks may have access to other info thats not on the report(eg c/c details if card is with said bank).
If you believe this is a mistake, I would contact the bank in question and advise them that you believe there is a mistake. Perhaps they will advise you.