Calling $webclient.UploadString in .NET Framework 2.0

I seem to be having a challenge retrieving $results using $webclient.upload parameter. This snippet of code was transferred from a server running IIS 6 with a web service running .NET 1.1 . It's launched through powershell on a IIS 7 server running .NET 2.0. The error I am receiving seems to point to the version of .NET but I'm not entirely sure. Any suggestions?

SNIPPET OF THE CODE (PS1 script)

$webclient.headers.Add("Content-Type", "text/xml; charset=utf-8")
#$webclient.headers.Add("Content-Type", "application/soap+xml; charset=utf-8")
$WebClient.Proxy = [System.Net.WebRequest]::DefaultWebProxy;

$WebClient.Proxy.Credentials = [System.Net.CredentialCache]::DefaultCredentials;
#$result = ([XML]$webclient.UploadString($Url, #

$soapMessage)).envelope.body.GetPISummaryDataResponse.GetPISumrrayDataResult

$result = $webclient.UploadString($Url, $soapMessage)

ERROR RECEIVED

Exception calling "UploadString" with "2" argument(s): "The remote server retur
ned an error: (500) Internal Server Error."
At E:\scripts\SummaryCalls452b.ps1:83 char:34
+ $result = $webclient.UploadString <<<< ($Url, $soapMessage)
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : DotNetMethodException