There is a new document available to help you debug Order Import in Order Management: 

The white paper addresses debugging from a technical perspective. This approach is to assist users in understanding the actual issue, as well as help them in the early resolution of any order import issue.

It will walk you through several cases, with supporting debug logs / trace files taken for each case. Educating you along the way for what debug logs / trace files should be gathered, as trace files are not always needed.  It will also walk you through the supporting documents so you will know what to look for in your case.

Please refer to this note the next time you have an Order Import error. Or you could step through it now, so you are informed the next time you encounter an Order Import error.  Happy debugging!