I use a Juniper VPN in order to connect to a remote network. Since upgrading to OS X Yosemite, I found that I could no longer connect to the VPN. Normally, I would launch the application, Network Connect; enter my credentials, and bam! With the new version of OS X, Network Connect would hang when trying to establish a connection to the remote network after enter verifying my credentials.
The issue lies within Yosemite's driver policies, where all drivers need to be signed now. In Mavericks (10.9) drivers installed to /Libraries/Extensions needed to be signed. If they are installed else where, such as /System/Libraries/Extensions or in the case of Juniper /usr/local/juniper/nc/8.0.7, they were fine. The only way that I was able to find is to turn off this feature, which isn't exactly the best option, but it's the only option until Juniper decides to sign their drivers.
Open up a terminal and run the following command:
$ sudo nvram boot-args="kext-devel-mode=1"
The command above sets the system into "development mode" where you can "test" the kernel extensions (kext). Again, this is not an ideal solution, but it works. This also works for other drivers as well, such as hard drive TRIM, sound cards, network cards, etc., any driver extensions that isn't currently being signed. To undo this type in the following command in a terminal:
$ sudo nvram -d boot-args