I just installed UpdraftPlus but when I select "Settings" in the Plugins page or through Settings > UpdraftPlus Backups, I get a "500: Internal server error" page.
I just found the answer...at least for people hosted on NetworkSolutions:
find this file:
and remove this line:
zend_extension = /usr/services/vux/php5/lib/php/extensions/ZendOptimizer_real.so
There must be some sort of conflict. I spent an hour pulling out my hair and thought it useful to pass it along.