A call to a Web Service can fail if is using the option 'EasySoap engine' instead of '.NET engine'.
There are several errors that can be returned, you can see in the EasySoap log for example:
HTTP/1.1 502 Proxy Error 'The specified Secure Sockets Layer (SSL) port is not allowed'
Error writing to secure socket, expected to write 1460 bytes, wrote -1 bytes
Reproducing the Issue
Call a Web Service via Web Service Proxy Wizard from PowerBuilder with option EasySoap engine (option .NET engine not checked).
PowerBuilder engineering have confirmed that this is a limitation: our EasySoap engine does not supportHTTPs
As the EasySoap will not evolve, the only way to access HTTPs is either to use the .NET web service engine.