Can't update old apps, or install new apps - 4.4

[snickersnee]

Android 4.4 on Nexus 4 was working fine. As of recently (today? yesterday?) I cannot install new apps or update old apps. In the Play store, the downloading bar just seems to sweep to the right like it's trying to get something. Which it likely is. Forever. Rebooting doesn't help. Otherwise, it seems to work fine. I've checked a bunch of other threads, and have tried
a) syncing my account in the settings.
b) checking that there's lots of space on my flash.

I'm trying to move my apps and data to my new Nexus 5, and was trying to use Helium for this, but haven't had success. In my attempts, I have used the ADB interface drivers on my PC, and connected a bunch of things, tried copying app data backups around but have tried to keep the source locations intact.

I'm open to suggestions. Pointers such as "you should have looked in this other place first" are welcomed, provided the info is pertinent and helpful.

Thanks.

 

[snickersnee]

I resolved the problem today by following the advice in the Google Play Store. The Apps section has a FAQ advising that these symptoms may be resolved by going to Settings -> Apps, scrolling to the right to see "All" apps, and then clearing Data and Cache for both the Play Store and Download Manager apps. I then had to log out of Talk/Hangouts and log back in. It took a bit of time for this to work (i.e. longer than the 30 seconds I was watching), but they'd all updated within an hour. I can also now install new apps.