Zoho Invoice not Importing

Hello,
I am investigating using Zoho Books. I am currently using Zoho CRM with Zoho Invoice. I have been able to import Customers and Items from Zoho Invoice but am importing Invoices fails without an error. Just brings me back to the upload file screen. I have tried .xls and .csv export from Invoice but neither seem to want to import into Zoho Books. Thanks for the help.