After many hours of debugging I found out that the gamesparks library does not raise an exception when an error occurs in a function that is invoked through NewHighScoreMessage.
Might I suggest that this will be implemented? I've searched for hours why something wasn't working when it turned out it was a simple nullreference in my code, but this error was never logged through the console because it occured via a callback from GameSparks.
Hopefully this is of help to anybody.
Can you give us some more details here please ? I've tested some code in the NewHighScoreMessage that generated an error that was logged in the script.log. It appears to be working fine for me. Are you able to replicate what you were seeing here originally ?