Method Community

I'm hoping someone can help me troubleshoot this issue, or wants some customization work, since I've hit a wall with my programming resources.

I am trying to access a payment provider (other than the Method list) by using their Web service API.  It seems like using the Web Service Call action would be just the ticket for doing this within Method, and then being able to update the account.  But when I enter the URL and the parameters, instead of the expected response, I get an error message: "The remote server returned an error: (500) Internal Server Error."  Val suggested in this thread http://www.methodintegration.com/cs/forums/t/1964.aspx  that I type the parameters into a web browser to see if they are correct, but that also returns an internal server error (a runtime error exactly)  The Web Service provider says that won't work, it has to be done programmatically.  Can anyone confirm whether the web service calls are being sent using some kind of SOAP routine?  

I also have the option of using a simple HTTP POST command to access the payment provider.  And I can get that to work using the Web Service Call action and their PostPayment.cfm page, BUT I need to send six parameter at a single time.  And I can't join more than one parameter together successfully (I need to be able to define which parameters they are as well as list them so a simple string joined by commas doesn't work)

Hope I'm making sense here and someone can point me in the correct direction or has a bright idea.  In the meantime we are building a separate web page to test the web service calls outside of Method, but that's just a testing mechanism, not a solution.

Thanks,

Victoria