Yuck, good catch. The function name has probably been wrong forever and the new handling of messages/response is a lot cleaner as well, so I will get both updated for the next version.
Both single and double quotes should work, but it wouldn’t surprise me if you ran into an issue either. Any other info you can provide would be great.
@twelve6 It looks like you are using the ACF 4 code which is starting to fall behind the ACF 5 development, so that is likely where you are seeing issues with the quotes. I would recommend upgrading to ACF 5 if you can.
Justin