I'm on day two of learning F# and I'm failing to understand this compiler error which I'm guessing is pretty obvious. After multiple hours of trying different approaches to resolve it I'm starting to get exasperated. I'm trying to create a function that uses WMI to update DNS CName records for an automation project I'm working on and keep getting the following compiler error on the last line of the function:

"Type constraint mismatch. The type obj is not compatibile with type unit. The type 'obj' is not compatible with the type 'unit'"

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let UpdateCNameDNSRecord(record:string, value:string) =
    let query = String.Format("SELECT * FROM MicrosoftDNS_CNAMEType WHERE OwnerName=’{0}’", record) in
    let scope = @"\\.\root\microsoftdns" in
    let searcher = new ManagementObjectSearcher(scope, query) in
    let inputParams:Object[] = [|null; box(value)|] in
    let moCollection:ManagementObjectCollection = searcher.Get() in
    let moArray:ManagementObject[] = [||] in
    moCollection.CopyTo(moArray, 0);
    Array.iter(fun(x:ManagementObject) -> x.InvokeMethod("Modify", inputParams)) moArray

VS2008 is pointing at InvokeMethod(Modify, inputParams) as the culprit. I've gone through several iterations of this function originally using IEnumerable to create a typed squence etc.... but every implementation results in the same error.