I have recently upgrade my Sony Xperia Arc S to Android ICS and been facing a problem with downloading from Google Play when using mobile network. It pops up 500 download error message.
After a couple of attempts to search on google and forums, finally I have found a solution.
Just remove the proxy address from your APN settings and reconnect your data traffic and it works for me. To change the APN settings, go to Settings > More > Mobile Networks > Access Point Names and choose your currenly used access point. You can empty/remove your proxy address there. If this doesnt work you can also try to remove and readd the access point.
A couple of other solutions I found on the net which doesn’t work for me :
– clear the cache and/or data of google play application (can be done through settings > apps> google play store)
– reformat SD card (haven’t tried yet)
– connect to wireless network first before reconnect to mobile network
– change content filtering (http://talk.sonymobile.com/message/185982)