This particular error happens when Skynamo QuickBooks app fails to connect to QuickBooks. As the error is temporary, another attempt to resubmit the order will be made on the next cycle.
To resolve this issue manually, the following can be attempted:
1) Search for Skynamo in the Task Manager and kill it manually
2) Check for any QuickBooks error boxes and close them
3) If this fails, a restart of the QuickBooks Desktop server might resolve the issue.
Failing this, please send a mail to firstname.lastname@example.org to request intervention from the support desk.