Nick,
As promised, I am attaching a copy of the email I previously sent you since it may help others that may encounter the same problem.
Nolan

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We spent quite sometime troubleshooting the problem. Since we not really have any source code, we can only do some process of elimination work. This may be old news to you but we fixed the problem by closing open reports or windows in QB. Exiting from QB and restarting it without closing the windows is not going to fix the problem since when you restart QB, it will launch all previoulsy open windows and bring it to a state identical to what it was before exiting QB. The interesting thing is, even if you configure the Order Export to import into QB by pointing to a QB data file (QB not running), the result was still the same: it will not write the transaction to QB and get the error message saving.

Note also that rebooting the whole computer does not also fix the problem.

Again, just for people who may encounter the same situation. The problem was fixed by closing open panels, windows, or reports in QB. I think it is record locking issue but the message gives no hint of this.