[Galaxy S II Q&A, Help & Troubleshooting] bnapalm:
Hello everyone!

Although I am not using GS2 (I have a Galaxy Note), I chose to post here because I didn't want to create a new post and I believe this is not a device-specific issue (see below for why).

I have the exact same problem as OP (as far as I can see). When I got my note less than a week ago, everything was working great. Then, last Friday I noticed that I cannot download anything from the market. After choosing to download something (both paid or free), after clicking "accept & download" at the permission screen, the screen goes back to app screen and market shows the app as "downloading..." with working, yet empty, progress bar. Everything else using the internet works fine - browsing from different browsers, notifications, email etc. I even tried installing an alternative market app, and it would download/install apps no problem. Also, downloading straight .apk files works as well. Later that evening I also noticed youtube app doesn't work - just the "loading" circle keeps running, until it times out. Browsing/searching market/youtube works without a problem. I am using the stock ROM and it isn't even rooted. Later, following some suggestions from google searches on the problem, it turns out that downloads work when I disable network and let it use mobile internet. I also later found out that it works on other wifi networks, just not my home wifi (which used to work perfectly, with no configuration changes to the router).

Next day I also found out that my girlfriend's android (LG Optimus Me P350) has the same exact problem, therefor it is not a phone model specific problem.

Here is what I tried so far:

Factory reset - left me with no apps and no way to re-download them. The market download did work ONCE after the reset, but that was to download the update to the market itself, nothing else;

Clearing Download Manager data - worked for ONE download. At first it worked for one download every time, meaning, after clearing download manager data, I was able to download one app, after that it would go back to the problem. I could then clear data again, and it would again download one app. After about 5 apps downloaded this way, this solution won't work at all anymore;

Force closing/clearing data of market, gmail, talk (in combination with above step) - didn't work;

Signing out/in to gmail and/or talk - didn't work;

Changing google account in market - didn't work;

Stopping/starting download countless times - didn't work;

Switching wifi on/off - only starts downloading briefly when phone switches to 3G while wifi is off. As soon as it gets wifi connection back, the download stalls at the position it was until I switch wifi off again (so it can continue to use 3G);

Switching phone to airplane mode, off/on, then disabling airplane mode - didn't work;

Changing phone's DNS records with an app to OpenDNS - didn't work;

Updating router firmware - didn't work;

Resetting router firmware - didn't work;

Setting port triggering on router for port 5228 - didn't work;

Port forwarding to Note IP for same port - didn't work;

Disabling router firewall - didn't work;

My router is Linksys E1000.

I think that is all I tried. I have been trying to find a solution for the whole weekend, and nothing as far. Searching google makes me believe that many people have had the same problem. I have found many solutions, which don't work, or only work once. This problem is really, really irritating. Also, I have found out that for many people the problem seems to randomly disappear without doing anything after some time (days to months), sometimes coming back and sometimes not. I experienced this myself when after going to sleep, I was able to download one app in the morning with no tried "fixes" at that time. This also makes me believe that there are many "fake" solutions, which did work for some people, but not for others - quite possibly, while these people were "solving" the problem, it actually solved itself, yet because the person did something, he/she believes that was the solution. A notable example of this could be "google account 24-hour reset" where users experiencing the problem are suggested to log out of their google accounts everywhere and not use the account for anything for 24 hours. Seeing as this is possibly a problem somehow connected to another device, not just the phone itself, I did consider flashing DD-WRT on my router, but I wouldn't really want do do that since my router is not that powerful and with all the DD-WRT features my broadband speed gets capped at about 65Mbit/s. Still a lot, but I have a great internet connection and am able to get real speeds of about 90Mbit/s with stock router firmware.

If anyone has any ideas, please share :) Thank you in advance!