What kind of device are you using? I looked into the 403 error you are receiving and it looks like an issue on Google's side. Google has been having some issues with the conversion to GooglePlay.
Try clearing the proxy and see if this fixes it:
Settings / Wireless & Networks / More... / Mobile Networks / Access Point Names (APNs) / MOWAP / Edit Access Point screen
Please try that and let me know if it resolves the issue.
Thanks!
(By the way -Thanks for your help ProTruckDriver! )
The solution I've tracked down for you is a bit on the complex side, but you could try what is suggested in this YouTube video. Ultimately you may want to contact Google support. George is correct that this is an issue on Google's end.
/// JimM /// /// Co-Community Manager /// /// Formerly a Technical Support Escalations Engineer ///