Searching through the forums I see that a lot of people problems getting 1Password to work with Sparkasse online banking sites, since they seem to use random field names that change every time you enter the site. The same is true for my local bank, the Sparkasse-Harburg-Buxtehude. 1Password appears to fill the fields for Username and Password, but authentication always fails.
At least they have a test account page where 1Password also fails. Maybe the developers can take a look at it...
, then click on the Demokonto link.
Username: smsDEMO, password 12345