Error attaching file to custom record w/.Net

We are currently trying to attach a file from the file cabinet to a custom record using the SuiteTalk web service when a specific action occurs in a product we have developed. 

I can't find a lot of documentation on how to do this, but I think what I have below should work, however, when calling the "attach" method, an "unexpected error" is returned.

Here is the code snippet:

            CustomRecordRef crImplementation = new CustomRecordRef();
            crImplementation.typeId = "28";
            crImplementation.internalId = implementationId;
            crImplementation.name = "customrecord28";

            RecordRef fileRef = new RecordRef();
            fileRef.internalId = "10828";
            fileRef.type = RecordType.file;
            fileRef.typeSpecified = true;

            AttachBasicReference attReference = new AttachBasicReference();
            attReference.attachedRecord = fileRef;