I did some searching around... from frontersupport.com:
* What are the different room export options? tests will be in an IMS format that can be imported back again.
* What can I export from tests? This export will provide you with an IMS QTI XML file.
So basically, Fronter exports tests in IMS QTI format (saved as an XML file).
Moodle, in turn, uses a "propietary" format (a very comprehensive one), and I'd say that's why you are getting error messages. It seems that even Fronter has limitations importing test questions ("there are some known limitations currently in the test tool's support for importing questions from an XML file -IMS QTI").
Looking around in the Moodle Docs, I just found that since version 2.3, under the Blackboard section of the Import questions page, it says that "both Blackboard POOL and QTI files are supported":
However, that leads me to think that the QTI file would have to be in a binary format. I guess you'll get more help about this at the Quiz forum.
Finally, I found this online tool: QTI Converter, "you can convert a QTI XML file or a .zip file containing a single assessment into a SCORM 1.2 package using this interface." You might want to give it a try.
From jqti.qtitools.org, "QTI XML is rather unlike most xml documents as it doesn't only contain data, but also instructions."