Following this post viewtopic.php?f=18&t=463, it looks like software upgrade (from one version to another version) requires a special attention under Windows 7 64bits. Usually, you have to execute a "Windows software uninstall" procedure of old software version, and then you can install the new version. It appears like, after "uninstall" procedure, Windows 7 64bits requires to manually erase the software folder before installing the new software version.
We are not 100% sure about this. If you already had the experience of upgrading our software under Windows 7 64bits, your feedback is welcome.