On Tue, 12 Feb 2008 09:24:11 -0800 (PST), Steven
wrote:

My garage door opener can open smoothly, but it only closes about half
way - seemlingly encounters resistance - and then the door re-opens.
I disconnected the automatic opening system and tried to close the
door manually - it worked but I could feel resistance when pulling it
down around half way. The system seems fine - springs, cables,
rollers, etc. (I just installed a new SEAS garage door opener two
weeks ago and it worked fine until two days ago. It's an old door
abotu 15 years old and the old garage door opener was replaced. I
also lubricated the components of the garage door system.)

Any suggestions? Thank you.

In addition to the other suggestions take a look at the garage door
opener track. If it's a two piece track the connection in the middle
may be misaligned and cause a hiccup in the middle.