I have gotten that error message when I incorrectly added and modified a variable to my title and it appeared in the mobile output (when I tested on an iPhone). I believe I added the CMI_Completion Status variable but that is only for SCORM 2004 outputs.
Are you working with a published SCORM or API (xAPI) project?
Which variable are you using in your title track the passing score?
I would recommend using the AICC_Lesson_Status variable to tell the LMS that the training is completed
I would recommend using the AICC_Score variable to tell the LMS the average of all the test scores in the title
I am not sure if it is the same for an xAPI output…
Go through the variable manager and read each of the descriptions for the Reserved variables- that also helps.