I installed 6u10 b23 beta.
I setup xml files and registry entry to auto update to 6u10 b26 nightly build.
Clicked Update Now in Java Control Panel.
It started to install (really uninstall of b23).
I clicked cancel.
The MSI uninstall cancelled, but the online wrapper did not detect / handle an error code.
It ran the b26 nightly build which displayed:
"Another version of this product is already installed.
Installation of this version cannot continue. To
configure or remove the existing version of this product,
use Add/Remove Programs on the Control Panel."
See attachment.