Hey Guys,
I just wanted to share my experience with you all and hope it will be helpful. I have Note 3 updated to lollipop but I believe all Android phones are similar.
First of all ANDROID IS CRAZY "Literally", you will not understand when the problem will happen to your phone and how to fix it, especially that the problems may be interrelated, and one fix may not be enough until you know really what is wrong with your phone.
Now to the subject, my phone was getting this "unable to download" error message, then same time suddenly from no where I get an error on the notification menu "sign-in request" with Gallery Picture beside it, and when I click on this message it requests to log in with Picasa and then all google applications disappear from the phone, and when I go inside "Apps" (on the bottom right of your phone desktop) I found them disappeared from the inner folders of Google, then suddenly out of no where all apps get redistributed over the pages within Apps and Google Apps return back again distributed also. All of this besides when I was restarting the phone it was taking around 5 minutes to open phone's desktop.
To fix the above I made Wipe data and factory reset more than 5 times in 2 days with no result.
Then after some search I did the below fixing (after one more factory rest):
1- Went to Settings - "General" Tab - Accounts - Google then click on the e-mail beside the Sync symbol, then scroll to the end of the page and uncheck "Sync Picasa Web Albums".
2- Went to Settings - "General" Tab - scroll down to About Device - click on Software updates then uncheck "Wi-Fi only". (Of course this is going to charge if not subscribed to mobile data package).
3- Went to Messages - click on menu - Settings - Multimedia messages, then uncheck Auto retrieve.
4- Activate "Mobile Data" from notification menu and disable Wi-Fi.
5- Restart the Phone.
All of the above fixed my problems, but again we have to remember, Android is crazy, at least for me.
Hope this is useful to somebody out there.
Thanks
Sameh Adel