sesquilia

I undid the P trap under my bathroom sink to clear a clog and now when I put the whole thing back together it leaks out of the top of the slip joint that connects the down pipe from the sink drain to the j-pipe. The down pipe is 1 - 1/4" and the j-pipe is 1-1/2" and I am using the correct reducer gasket. It was not leaking (and never had) before I took it apart. I have tried using a new gasket and teflon tape on the threads of the slip joint to no avail. Please give me some idea as to what the problem might be. Here is a link to a couple of pictures to show the general set-up and the specific problem:

http://www.flickr.com/photos/sesquilia/?saved=1

Thanks to anyone that can help.