It seems the popup originates in lms.js, lines 236-243.
My guess: the lms gives back an error through g_oScormApi.LMSGetLastError(); which it maybe should not do.
Somehow the lms is not happy. Why? I don't know but it might be your quest for the days to come

- You could write your own popup to check the value of g_oScormApi.
- You could use the Reload Scormplayer to check the communication with your sco i.e. to check your sco.
- You could test/check your module at http://testtrack.scorm.com/ (before use read the conditions!)
- or download the diagnostic scorm package at http://www.ostyn.com/standards/scorm/samples/proddingSCOwrap.htm and install it in your lms (not easy to use).