Error using Decimal value with MailChimp and PerceptiveMCAPI

When calling the MailChimp listBatchSubscribe method via PerceptiveMCAPI in ASP.NET, I got the followng error:
“A parameter is of, or contains an instance of, type CookComputing.XmlRpc.XmlRpcStruct which cannot be mapped to an XML-RPC type”
I panicked, thinking that the PerceptiveMCAPI, which up to now I’ve found flawless, might be broken for this one, vital method. Was it unable to process the Dictionary it required as input?
After looking closely at my merge vars I commented out one that had a Decimal value. Everything magically worked. Replaced with a double and I’m back on track.