It could be one of a few things:

1.) I think they disabled (for a short time) intercity commerce when they were applying the hotfixes to the servers. (A friend and myself were just playing and did the exact same thing and it worked)

2.) The workforce requirement and the actual workforce don't match. What I'm saying here is, if you have high tech industrial, you need educated middle to high class workers. If its all "dirty" (low class) industrial, you need all low class. If it's a mix, you need a mix.

3.) (Unsure if this is true or not) If you own both cities, the residents wont commute because the city is inactive whilst you're playing the other. (Once again, I doubt this is true but I've heard it before.... It doesn't seem to happen to me when my friend is offline, my people still commute to his cities.)



If I were you, I'd restart. (I know, that sucks), but with all of the patches coming out and all of the server interruptions, it could have affected your region somehow. I had an incident where all of the trade between my cities was broken due to the new patch, restarting the region fixed it all.