LCS Communicator 2005… won’t re-install

Short version: I broke my communicator 2005 client install and now I’ve found how to fix it.

Long version: We are busy planning an LCS to OCS upgrade, and as usual we are staging it in the dev environment to see how things go. In doing so I shot myself in the foot…

So, I’ve avoided fixing the issue for a few days, but irritation and need have reached a point where I HAD to fix it.
I’d messed around with patches for communicator with the intention of applying them to a dev environment. I went ahead and installed the ‘Communicator 2005 hotfix rollup package: December 19, 2008’ patch KB949280.
I also installed all the post SP1 2005 patches on the test/dev LCS server we had. I then successfully connected to the dev server with said client and was happy.
I then flipped the local client config back to our prod (unpatched – SP1 only) server and couldn’t connect using TCP/TLS, auto config or manual. Nothing – ‘Cannot connect…’

I uninstalled KB949280, rebooted, all to no avail. So I uninstalled Communicator, again rebooted and tried to get it re-installed. Despite numerous attempts at install as a variety of users, using the runas to launch it or even explorer.exe as ‘Administrator etc, I got the same message: “This installation was interrupted. No changes were made to your computer system. Please try running the installation again.”

I gave up for a day or so at this point as I had other things to resolve that were more pressing than my own client.
Today, a problem of a different sort has meant I had to find a way to get online from my laptop.

I started googling ANYTHING that popped up for LCS, and out of all the nonsense, I found KB974571, which is a patch that is very useful in fixing LCS/OCS when the server won’t start, but it’s also installed as a standard Windows update on workstations (XP). I looked through my patch list (in add/remove programmes remember to click ‘show updates’ in the top of the window) and found it installed. I uninstalled it (despite there being a big warning saying loads of other patches will break) and rebooted.
I re-ran the installation msi and presto it installed! I logged in, messaged a few people. I then re-installed KB974571, rebooted and all remains well, I am logged in and sending IM.
It’s old software, but works. Look out for my OCS install notes in a future post.

-Luke