I have an external .NET WCF Service that I am trying to invoke from outside the Salesforce sandbox.  One of the arguments in the .NET WCF Service function call is a byte array.  What is the appropriate conversion in APEX so that I can pass data to this function?

WSDL element:

<xs:elementminOccurs="0"name="FileContents"nillable="true"type="xs:base64Binary" />

Call to this:

String filecontents = BuildFile();
inputfile.FileName = 'SalesForceAddressFile.txt';
inputfile.FileContents = EncodingUtil.base64Encode(Blob.valueOf(filecontents));

When I look at the DataContract that was pulled in, the property is a String, but defined to the service as base64Binary.

Here is the DataContract code that was generated from the WSDL:

    public class FileObject {
        public String FileContents;
        public String FileName;
        private String[] FileContents_type_info = new String[]{'FileContents','http://www.w3.org/2001/XMLSchema','base64Binary','0','1','true'};
        private String[] FileName_type_info = new String[]{'FileName','http://www.w3.org/2001/XMLSchema','string','0','1','true'};
        private String[] apex_schema_type_info = new String[]{'http://schemas.datacontract.org/2004/07/CDITecServices','true','false'};
        private String[] field_order_type_info = new String[]{'FileContents','FileName'};
    }

But when I invoke the webservice, there is an error thrown and I have narrowed it down to this property.  What am I doing wrong?  I have UnitTests setup in an external program that test the web service outside of the call from SalesForce, so I know that the webservice functions properly.  If I set inputfile.FileContents to null, I can get from SalesForce to the web service and execute the web service method.  When I keep the code as above, and send a String using the EncodingUtil, it errors on the invoking of the web service method.