VB.NET System.IO.IOException: The handle is invalid. when passing a string to a web service

Passing a text string to an external web service, I intermittently get a 'handle is invalid' error, roughly once every 30 times or so. Every other time it sends with no issue.

Can't post specific code but the gist is the following: 1) Create and build object to send to service 2) Instantiate proxy object 3) Call the web service proxy, attachMessage method.

Stack trace is as follows:

Process Exception: System.IO.IOException: The handle is invalid.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.WriteCore(Byte[] buffer, Int32 offset, Int32 count)
   at System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count)
   at System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder)
   at System.IO.StreamWriter.Write(String value)
   at System.Diagnostics.TextWriterTraceListener.Write(String message)
   at System.Diagnostics.DelimitedListTraceListener.WriteHeader(String source, TraceEventType eventType, Int32 id)
   at System.Diagnostics.DelimitedListTraceListener.TraceEvent(TraceEventCache eventCache, String source, TraceEventType eventType, Int32 id, String message)
   at System.Diagnostics.TraceSource.TraceEvent(TraceEventType eventType, Int32 id, String message)
   at Microsoft.VisualBasic.Logging.Log.WriteEntry(String message, TraceEventType severity, Int32 id)
   at Microsoft.VisualBasic.Logging.Log.WriteEntry(String message)

Any assistance would be much appreciated!