Problem when calling a web service from workflow

Hi,

I'm working on CRM 2011, and I try to call a custom web service function from a custom workflow, but this fails while trying to access the web config file, although this file exists in the given path and there is a reference to that service.

After some googling, I've found this:

https://msdn.microsoft.com/en-us/library/ms735898(v=vs.85).aspx

I didn't use "InvokeWebServiceActivity" in my code.

My question is: what is the best way to call a web service function from a workflow? If an example could be given - it would be awesome :)

Thank you.