Meetings created in EWS RTM Format can not be updated using EWS SP1

I tripped across an issue when trying to use Exchange 2007's Exchange Web Services SP1 to update a meeting that was created in the RTM version. I could not. Here's the error message:

The EWS Id specified is in Exchange 2007 RTM format while your request was made in the Exchange2007_SP1 mode. Please use the Exchange2007 SOAP version header in your request or remove it, or use ConvertId method to convert Id from EwsLegacyId to EwsId format.

The issue -- Exchange changed the EWS identifier format from Exchange 2007 RTM and SP1. ConvertId is required to convert the "EwsLegacyId" to the "EwsId". The change in identifier format is well documented. We don't typically update old meetings, so we haven't come across this issue before. Here's the link to the ConvertID page on MSDN:
http://msdn.microsoft.com/en-us/library/bb891865(EXCHG.80).aspx

and sample C# code: http://msdn.microsoft.com/en-us/library/bb856559.aspx
-Russ