This error is caused by the lack of defined periods for the year 2013. The bank statements file I was trying to import has references to both 2012 and 2013.

The import needs periods for all the references in the bank statements file. When I imported the file the periods for 2013 where not defined.

After I defined the periods for 2013 the problem was solved.

This can be done going to:

accounting/configuration/fincancial accounting/periods/fiscal years (or periods)