Hello! I am very sorry you're having trouble updating your Nuvi 2450. I know how frustrating that can be, especially after waiting for a long time for the download of the new maps to complete.
The main reason this problem occurs is when folks try to (rightfully!) use Garmin's "lifetime updater" application.
Unfortunately, it does not work correctly. Here are some other things to check, also...
First, please make sure you've disabled all antivirus and firewall software on your computer. Second, please make sure the Nuvi is the *only* USB device plugged into your computer (aside from your keyboard and mouse)...finally, please use the "one-time" updater ("Option 2") instead of the lifetime updater...if you have a lifetime map update subscription, it will not be affected by using the one-time updater application. It is just a different updater that actually works. :-)
I've also written detailed instructions for the one-time updater that I can post if you need them...if so, please let me know and I will post them ASAP.
I hope this resolves the problem for you...please let me know if you have any other questions and I will do my best to help further.