The typical cause of this error is that you flagged one or more fee/expense transactions “Off Invoice” but the Bill Amount field on those transactions is greater than $0.00.  To check for this, go into Time Manager and set your Fee Filter to capture all the fees that would have been billed on the Invoice in question.  Right click and choose Select Grid Fields.  Drag and drop the “Off Invoice” field into your column header.  You now want to look for any transaction where the Off Invoice field has a check mark in it.  You are going to go through the same steps in the Expense Manager to find anything set for Off Invoice.  If you find any transactions set to Off Invoice you will need to void the Invoice and call back up the Client-Matter in Bill Prep. Remove the check mark from Off Invoice on the appropriate transactions and re-create your invoice.

NOTE:  If the Off Invoice feature is not the problem, you will need to contact Orion Support.