Please refer to http://labs.seapine.com/TCMScriptAgent.php.
The .trjob file contains an entry "MainResultFile", which should be filled in by the script agent application with the name of the result file generated by QA Wizard. This file should be in the same folder as the .trjob file. The TestTrack client uses this entry in the .trjob file to know what file should be loaded and attached to the test run as the result file attachment. The error you are reporting means that either this entry in the .trjob file was not filled in or that the file referred to by this entry was not found.