Jay, don't worry about the three ways to create a server key. I'm getting the same error message yet I can use verisign.so just fine. Be sure to edit the Makefile for this library and the verisign.c file.
For test purposes you'll have to change
char *hostAddress = "payflow.verisign.com";
to
char *hostAddress = "test-payflow.verisign.com";