If is Android Market Errors - such as downloading apps or installing then try this below. I have a Samsung Note 1, but it also worked on my friends S2, S3, Galaxy Note 2. Is just deleting the Access Point Name:
Step 1: Go to Settings > Mobile networks > Access Point Names>
(then click into your mobile/network provider)
EG: AT&T, Optus, Vodafone etc etc.
Step 2: Click into PROXY, then write down the proxy number on a paper, then remove the proxy numbers so that it's blank, then press OK.
Once you've removed the proxy details, u should able to download apps from the Play Store. You might need to restart your phone before the changes take effect.
Keep that proxy number you wrote down or save in your phone as a message. This will help you if there's any changes needed if phone updates.
Hope this helps