The rubber between roof and windshield is off

Last week I replaced the front windshield of my Maxima 2000. There was some rust on the front side of the roof and water used to leak inside. I did that too.

I tested the whole thing by driving at 120 km for a short time and washing the car, and everything looked OK.

yesterday, I drove for about 1:30 hours at 120-140 km and when I reached my destination, I noticed the thing in the attached pictures.

Before I take it back to the repair guy, I'd like to find out from you what might have happened and what should he do to fix it.

I'm sure you've taken care of the problem by now, but other folks may be interested in a reply. Best I can tell from your photo, you needed a new windshield gasket as the existing one looks worn with age and ripped on the edge. It should fit in the channel securely unless rust has mucked up the fit. If the windshield channel is messed up, you'll want to first arrest the rust and apply rust inhibitor. You can then use 3M Black Super Weatherstrip Adhesive to make sure the new gasket stays in the groove.