Object reference not set to an instance of an object.

I submitted a cart and received this nondescript error message back from SOA.

Does REST/SOA produce detailed logs that we can inspect upon such an error?
I tried editing the Scheduler web.config, to log at an INFO threshold as follows:

<appender name="FileAppender" type="log4net.Appender.FileAppender">
        <file value="..\Asi.Scheduler_IMISDemo.log" />
        <appendToFile value="true" />
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%d{yyyy'-'MM'-'dd HH':'mm':'ss'.'fff} %p %t %c - %m%n" />
        </layout>
        <filter type="log4net.Filter.LevelRangeFilter">
          <levelMin value="INFO" />
          <acceptOnMatch value="true" />
        </filter>
      </appender>

But I didn't see any error messages when I experienced the Object reference error in the API. Is there anyway we can drill down when we receive general errors such as this from the API?