Sorry, this was my mistake. I forgot to put the Parameter "NULL_AS" in the Advanced Settings tab of tGreenPlumGPLoad.
Worked well after that.
I am getting the same error when exporting from a mysqlinput component to a postgresqloutput component. The connection setting ahs the string delemiter set to ' (single quote). Any suggestions where to look. Swapping out the postgresqloutput component for a text file works fine.