System Information
Operating system and graphics card
Mac OS High Sierra - v. 10.13.6
AMD Radeon R9 M290 2048 MB Graphics Card

Blender Version
Broken: (Blender 2.8 d022794cad9)
Worked: (2.79)

Short description of error
Error happens when using Environment Background image attached to Texture Coordinate Node -> Mapping Node. The background turns pink as if the image could not be found on disk. These extra nodes allow the environment to be rotated as needed. Worked properly in 2.79 without any difficulties. Without the Texture Coordinate and Mapping Nodes, the environment image shows up properly.

Exact steps for others to reproduce the error
Set up Environment Image Background in the World tab and attach an Texture Coordinate Input node to a Mapping Node and that attaches to the actual background image node.