I've tried to invoke a web service hosted on Mashape from my tibco design and i've received this error Failed to create secure client socket: Server certificate rejected by ChainVerifier
I've also tried solution posted by nathan but it didn't work.
Tibco designer console log: http://pastebin.com/iBhGHN4a
if you look at the certificate that Mashape is using you can see that it has also a Root and an intermediate certificate.
You need to ensure you have all 3 of them in your trusted certificates folder.