There are two reasons for seeing this message when attempting to upload a bank statement CSV.
The first reason could be that you are trying to upload a bank statement dated inside a closed financial year. That is to say that at least one entry on your statement is dated in a period which has had its year end documents produced and has thus been closed by your accountant.
The second reason could be that you are attempting to upload a bank statement dated inside a back dating period, i.e. before we take over your accounts.
In both situations given above, the solution is to remove any entries from your CSV which are dated prior to the date displayed in bold in the error message - Aug 2007 in our example above. You can remove entries from a CSV using a program such as OpenOffice Calc, Microsoft Excel or Notepad.