Powershell, System.Diagnostics.Process and asynchronous reads

Hello all,

I am trying to launch a process and grab the StandardOutput and StandardError using EventHandlers and BeginOutputReadLine.  I can launch the process but I get

Exception calling "BeginOutputReadLine" with "0" argument(s): "Cannot mix synchronous and asynchronous operation on process stream."

Here is my launch function:

Function Launch {
 if ($Global:Filename -eq "") {Throw ("Error: No Filename was provided!")}
 
 Write-Host $Global:Filename
 
 $ProcessStartInfo.FileName = $Global:Filename
 $ProcessStartInfo.Arguments = $Global:Arguments
 $ProcessStartInfo.UseShellExecute = $False
 $ProcessStartInfo.RedirectStandardOutput = $true
 $ProcessStartInfo.RedirectStandardError = $true
 
 $Process = [System.Diagnostics.Process]::Start($ProcessStartInfo)
 $Process.EnableRaisingEvents
 $Process.add_OutputDataReceived($Function:ReadOutput)
 $Process.add_ErrorDataReceived($Function::ReadError) 
 $StandardOutputStreamReader = $Process.StandardOutput
 $StandardErrorStreamReader = $Process.StandardError
 
 $Process.BeginOutputReadLine() # <--
 $Process.BeginErrorReadLine() # <--
 
 $Process.WaitForExit()   
} 

Am I violating the Powershell threading model?  Thanks!