Hi,
I had the same issue before (with Kirby 2.1), and it happened on different servers (not very low-cost, but also not very high-end).
Even my local XAMPP server (newest version, newest PHP installation) gives this error.
I will setup a test-case and send you the panel- and ftp-credentials -> but I can not alter the php.ini / php.config on that server (which may be the problem - but not all hosting providers allow you to alter these settings).
Thanks in advance!