microEC2 instance types have only half a CPU or less, which is usually not enough.
https://public.opencpu.org/ocpu/github/:yourname/:yourpkg/www. Let us know by twitter or email that you would like it published, and if it meets the minimum requirements, we'll fork it into the OpenCPU github organization.
/var/log/kern.logon your system and search for lines containing "APPARMOR" and "DENIED" to diagnose if this is the problem. The section on Customizing the security profile in the PDF server manual contains more information.
knitris currently installed on the demo server, navigate to https://public.opencpu.org/ocpu/library/knitr/. OpenCPU is an R package like any other, so to find out which version of OpenCPU a server is running navigate to https://public.opencpu.org/ocpu/library/opencpu/.
For (short) questions, you can also ask
@OpenCPU on twitter.