I googled this search string
nextgen gallery exception thrown error message
and found several results related to nextGEN Gallery. There are so many possible reasons this is occurring it seems difficult to isolate the cause. However, it is possible that the problem is in the NextGEN Gallery code somewhere.
@photocrati – Yes the problem did continue when I chose WordPress Twenty Fourteen as the default theme.
I then did a manual reinstall of WordPress, replacing the wp-admin and wp-includes directories (with plug-ins disabled).
Many issues have been resolved as a result of the reinstallation, but not the NextGen gallery problem. I reinstalled the basic NextGen gallery and still get the Exception thrown Error Message.
Looking forward to your reply. Thank you.
Terry Rich