Rtools not being detected by R

I had the same error, and I had installed the tool chain (I believe).

My fix was to move the R Tools paths to the front of my PATH variable.

Turns out when I installed RTools I left out the R 2.15.x+ toolchain option in the installation, which lead to the gcc never being installed. Hopefully, this post will serve as a diagnostic guide if RStudio fails to register RTools.

Thank you everyone for your help.

The RTools install on Windows doesn't select the C compiler to include by default. I ran the install a few times blindly clicking through and got this error. I reran the installer and selected/included the 32bit and 64bit C compilers. Problem solved.