Error while viewing SCORM activity to appear in a popup

While testing MDL-35870, Andrew Davis spotted following:

MDLQA-5248. If I set the activity to open in the same window it works fine. If I set the activity to appear in a popup I get a JS dialogue plus occasionally a PHP error. The PHP flashes up very briefly. It may always be happening but it happens so fast its only sometimes visible.
The PHP error is...
Could not find SCO
More information about this error
Debug info:
Error code: cannotfindsco
Stack trace:
line 463 of /lib/setuplib.php: moodle_exception thrown
line 154 of /mod/scorm/datamodels/scorm_12lib.php: call to print_error()
line 21 of /mod/scorm/datamodels/scorm_12.php: call to get_scorm_default()
line 258 of /mod/scorm/player.php: call to include_once()
The JS dialogue says...
Unable to locate the LMS's API Implementation.
LMSInitialize was not successful.