No, that is a warning and not a reason for your issue. The purpose of the warning is to tell you that this particular customer appears to have a collections issue.
I am quite sure that we can resolve your issue if we can get the appropriate queries run. I have a tool that allows me to connect to your computer or, in this case, your SQL Server box and I am willing to work with you and your IT person to run the appropriate queries to figure this out. I will do that at no charge to you provided that we can limit the time to 15 minutes. We should be able to do that if you provide the customer id and reference number of the invoice in question. I do not normally provide my services at no charge but this issue seems to be spinning it wheels quite a bit and it seems like this may be the best solution.