Thanks for your reply CharleneMae_F

I ran all the steps in the link you mentioned as step 3.

Step 1: I downloaded the CC transactions again for period May, selecting download type Quickbooks, which defaults to QBO. No error messages were triggered.

Step 2: I did not get any error messages when download my Capital One transactions.

Step 3: I already had tried to switch from Express to Classic mode in Change Bank Feed Mode. It did not make a difference, I still get the same error

Step 4: I created a new company file as suggested, I had not created the Capital Once account, just tried the import (as that normally ask what account the transactions should be assigned to), but again, I get the same popup.

I just have this one CC, thus, can't try another QBO import.

Would you have a sample QBO that I could try to import into the test company?

I am still puzzled why it worked once, then all subsequent imports triggered the same error right after starting the import.