Google Play Store download/update errors (Error 921 and -101)

I'm unable to download Apps or Update apps from Google Play Store. And i get these errors :-

1. if i'm trying to update i get Error 921
2. if i'm trying to download, it says, "unable to perform purchase" (and i'm just trying to download free app, not paid)
3. Tried uninstalling and rolling back to ver. 3.1.5 (as sme1 has mentioned this on xda forum), but then i get error -101.

*Solutions Tried * ---->
1.tried the method of unmouting the shared storage as mentioned here...
miuiandroid.com/community/threads/miui-rom-2-3-16-ics-gb-roms-uploaded.15733/page-14#post-113549

2. Clearing cache and data of Google Play/Market didnt help either.

Any help appreciated.

please, help people! :|

same issue, I resolved with

remove my google account, insert him back, clear cache and data for the google play store, kill all the active apps

Yes, Teoserio is correct, i had the same issue , and fixed it.. just remove the google account and add it again.. I neither clear the cache, just remove and add should fix that... i hope have helped.

Alright. Thanks for the reply. But i tried diffrnt method. i clean installed Miui(wiped cache and data) and before restoring the backup, i added google account and waited for 2-3 mins, it automatically downloaded google play.apk and updated. Then i did the restored backup. No Issues after that.

i hope from next version, Xiaomi updates all the apps(incld. Google Play) in the ROM. Then we dont have to wait for updates of basic apps like, Google Play, Maps and Youtube.

No need to clear but just remove the account n re enter again.

Can't seem to remove my Google account from the Play store without removing my google account from my entire phone. I can only add extra accounts. How is it done?

Ypou can only have one accoundt pr android phone, if you add extra they can sync mail contacts and calender but thats about it.

How to remove the google account?

Go to Settings>Accounts & Sync>*your google account*> click menu (on soft key)> Remove Google Account.

By the way the bove worked for me and removing my google account didn't mean I had to rejoin my contacts or anything, it was harmless.

Thank you black_mamba, my problem is fixed.