How to correct journal entries made into the wrong period

So, just ran Adjust cost - item entries report, and due to the fact that we didn't have Inventory Periods defined (or closed), we had over 1000 entries that were made in periods that should've been closed.

Now, I need to redo those entries.

I tried creating a Gen Journal with reversing entries, and correct entries in the current period, but I get an error because the dates on the original entry and the other entry have different dates.

Any idea what I should do? How can I correct this?

Thanks a lot,

Val