Hi, Juliet,
First, what version of Ledger are you using? You can obtain this information by selecting Help and About from the main menu. It sounds like you maintaining 2008/2009 and 2009/2010 in two separate datasets so it may be that you are using an earlier version that Ledger 9.0x.
When you say you 'exported it to 2009/2010', I'm thinking you mean you imported it. Was this a batch you imported? If it was then posted to 2009/2010 rather than being Post to Prior year, it would be reflected as additional transactions for the 2009/2010 period. Are you able to use the Post | Unpost function to unpost the batch from 2009/2010 and then Post | Post to Prior so that it gets reflected in te prior year balance?
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Regards,
Softrak Tech Support