I used the U760 for about 1 month with no problems. Suddenly the device would not power up when plugged into the USB port. Sprint sent me a replacement. It took me over 2 weeks to get the replacement working. After about 8 hours of phone support time with Sprint technicians who are absolutely helpless I was able to troubleshoot the issue. If the SmartView data connection software does not load from the device Sprint recommends you download the software from their downloads site. Well, the software on their site is a later version then on the card and does not recognize the device. This may be isolated to Vista SP1 which I am running. I manually installed the SV software from the device and now am connecting. Signal strength is not very good though.
The new software doesn't have issues preventing the U760 from connecting. It sounds to me like there was a corrupt file in the installation from the previous card that was conflicting with the new one. This is why I always recommend uninstalling the old software, restarting the computer, then deleting any folder that may be left in Program Files for Novatel, Sierra, or Sprint (depending on which software was installed and from where) before installing the newest version. It is not a problem with the software itself, it was probably a problem with that particular installation of the software on that computer.
We regularly use a laptop loaded with the latest software to troubleshoot whether it is the card itself that is having the issue or the installation (99% of the time it's the installation).