Over the last few days I ran into several puzzling ClickOnce deployment problems. I want to document and share these so that I’ll remember them better, and so others might find help with similar issues.

The first issue:
I uploaded new versions of my files several times, but every time I attempted to download the refreshed versions, no matter which computer I tried it on, all I got were old files. Ctrl+F5 in IE didn’t make a difference. Clearing the Internet Explorer history, cookies, temporary files didn’t make a difference. I even contacted my web host to see if they have any caching issues on the server side. In the end I stumbled across my installation of Fiddler, the HTTP debugging proxy. I looked at the raw HTTP dumps, and then I saw the issue: I’m behind an active caching proxy on my home network. The proxy was giving me old files all the time.
First issue solution:
Clean out the cache files on my proxy server. It happens to be squid, so this did it:

service squid stop
echo “” > /var/spool/squid/swap.state
service squid start

The second issue:
During the troubleshooting of the first issue I had started suspecting the ClickOnce caching system to be at fault. So I used “mage -cc” and “rundll32 dfshim CleanOnlineAppCache” to clean out the cache. No change. Then I started manually deleting files from the cache location on the hard drive. Bad mistake. Now I got weird deployment errors, talking about COM objects not being available, and “interesting” HRESULT errors: The referenced assembly is not installed on your system. (Exception from HRESULT: 0x800736B3). I uninstalled the .NET Framework 2.0 and 3.0 and reinstalled them. No change. Luckily I found an article on the MSDN forums that pointed me to a registry location to check out: HKCU\ Software\ Classes\ Software\ Microsoft\ Windows\ CurrentVersion\ Deployment. I checked it out and found a bunch of registry keys that I remembered seeing when I cleaned out the cache files before. So what would happen if I deleted all those keys? Maybe it would “reset” ClickOnce completely? Luckily it did.
Second issue solution:
Clean out both the ClickOnce cache files [C:\Documents and Settings\(User)\Local Settings\Apps\2.0] by hand (completely), and also clean out the registry keys under Components, Marks, PackageMetadata, StateManager\ Applications, StateManager\ Families and Visibility underneath HKEY_CURRENT_USER\ Software\ Classes\ Software\ Microsoft\ Windows\ CurrentVersion\ Deployment\ SideBySide\ 2.0

Caution! Your Mileage May Vary. Deleting registry stuff is dangerous! Make a backup first.