check the knowledge base for this issue.  There is a solution there that allows you to assign a number to the invoice and then you can clear it out.  I don't recall the article #, but that is how I found out how to solve that problem when I ran into it a while back

You can assign invoice numbers to those transactions by printing them.

Go to the Reports & Forms menu, choose Forms, then choose the appropriate type of form. When the "Select a Report of Form" window opens, choose the invoice or credit memo format you want to print and then click the Preview & Print button. In the next window, you can select at "through" date if you don't want to print all invoices/credit memos that don't have a number assigned (in Sage 50 logic, no invoice number = unprinted). At "Number the first invoice" enter the invoice number you want assigned to the first invoice that prints. Click the Refresh List button to see what it is going to print. Click Print/Email to print the invoices and assign numbers to them. If you don't want to actually print them, change your printer to Microsoft Print To PDF, or some other option that will let you print to a file. When it asks if they printed correctly, answer YES, otherwise the numbers won't be assigned.

Once the invoices/credit memos have numbers assigned, you can adjust them off in the normal way.

Thank you Tom and Stephen - Will print invoices - hope it works - thanks so much for the tips!

Just go to reports and forms and print them.