This is where it's unhappy:

[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://localhost/empire/LogUsage",
RequestNamespace="http://localhost/empire",
ResponseNamespace="http://localhost/empire",
Use=System.Web.Services.Description.SoapBindingUse.Literal,
ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public void LogUsage(System.Guid SiteID, System.DateTime Timestamp, int
PeakConcurrentSessions) {
   object[] oa;
   oa = new object[] {
       SiteID,
       Timestamp,
       PeakConcurrentSessions};
   this.Invoke("LogUsage",oa);
}

I broke this code (generated by importing a web reference) into three
statements so I could see which part gave it trouble.

   oa = new object[] {
       SiteID,
       Timestamp,
       PeakConcurrentSessions};

is what it doesn't like. This statement produces the exception "Invalid cast
from System.DateTime to System.Byte[]."

Any thoughts, people?