Usually when we release a new version, we change the ProductCode and leave the UpgradeCode intact. This way, when a user installs a new version MSI, the old version is automatically removed.
However, currently we're experiencing a problem where a version 1.1.26.10 is installed on a user's box and when he installs, 1.1.39.00, the old version is not removed. As a result, both versions are listed in Add/Remove Programs as separate installed applications.
We used Microsoft's ORCA applcation to look inside both MSI and confirmed that the product codes are different and the upgrade codes are the same.
Presumably the data in the Upgrade table is up to date? If so, you'll probably want to create an MSI log file and search it for information near the ISSetAllUsers and FindRelatedProducts actions, to see if MSI noticed the products are related...
