Nominal Codes

I am Treasurer of a Charity.  I need to send to Excel the individual transactions from "Activity" in the Nominal Ledger to prepare for the GiftAid Return.  For example, I did this for code 4000 yesterday.  However, wanting to do some more work on this today, for all the Nominal Codes I wish to send to Excel, the activity is completely blank, even though the total figure on the Nominal Code page is correct.  The "hide detail" and "show detail" at top left are greyed out.  How can I get to see the individual transaction for each Nominal Code again?  I have tried restoring back-up, but this has made no difference.  Any ideas please?