Do you have custom error handling setup on the web service call? With custom error handling you can write a message to the log with a stack trace, and then view it in the logs for the environment you are using. In the sprinter portal, if you click details on the environment you want, theres a button called "view current log".
Also, you can also adjust the log levels for certain nodes. If you go to the details of the environment, theres a tab called "log levels" and you can change the level from info to trace.
Here is a link to custom error handling documentation
I am able to see the error message using a breakpoint in the debugger, this seems to be reliable enough. Thanks!