Unable to upgrade iMovie via the app store

Hello all,

Mid-2011 13" MacBook Air with 1.7GHZ Intel Core I5 processor and 4 GB memory. OS is El Capitan (10.11)

App store tells me there is an upgrade for iMovie (currently running 10.0.9). Upgrade is 10.1. When I try to upgrade, I receive a error that reads "plist parsing error."

Is this an app store issue or is there something I need to do on this end to fix.

Thanks in advance!

Bob