A: When a document is uploaded to Live Meeting, it's actually "printed" into a Live Meeting format using the Microsoft Office Document Imaging (MODI) print driver, which is a 32-bit driver. 64-bit versions of Windows can't use 32-bit drivers, so they can't use this MODI driver to convert documents to the Live Meeting format.
To work around this problem, you need to upload the document from a 32-bit version of Windows (which could be a virtual machine on your 64-bit desktop or a remote desktop). Or, instead of uploading the document, share your local document inside the Office application.