I am having the same issue as the original poster.  I've tried all of the suggestions noted above.  None of our inactive items/customers/accounts have been changed in the past year or more.  We are not trying to use any of those items/customers/accounts, but still getting this error message.

I absolutely NEED to be able to create invoices.  I think this is a problem related to the QBO invoicing revamp that was released several weeks ago.  

What can I do to fix this if the above advice did not fix anything?