So, we were completely unable to install Juniper’s Network Connect client on someone’s Win7 box. The error number we got led to N completely different solutions that worked for some people and failed for us, which suggested that there were N different problems covered by that error number, and ours was N+1.
While cleaning things up on the box, I came across a Virtual Router package that was installed, which he wasn’t using, and which hadn’t worked anyway. Coincidentally (coughcough), around the same time more than a dozen additional network interfaces had been created in the device manager, none of them with names, drivers, or any useful detail.
I thought that perhaps the crudware had hit some arbitrary limit on the number of devices, and deleted the garbage ones and uninstalled it. Still no good.
Later that evening, the user did a little more digging, found a different error string, and followed it to this thread on the Cisco support forums, where a similar mishap was preventing a VPN install. The limit turns out to be 1024 network interfaces, and the vast majority of them were concealed deep inside the registry, with no GUI-visible hint that they existed.
An unofficial registry-cleaning script was created by someone at MS, and is linked in the thread, and that solved the user’s problem. I generally frown on running random Windows binaries linked from forum threads, but he was a consultant, and it was his own laptop, and he ran it before I found out about it, so…