Is anyone else having this problem still? I downloaded and compiled 4.15 preview 3, which lists this bug as fixed. When I load the Kite Demo on Linux (Ubuntu 14.04, latest nVidia 379.09 drivers, Pascal TitanX) using the default OpenGL4 renderer, I get the subject error. The result is the material won’t compile and I get the default material in the scene for some things such as tree limbs.
So the reason you are not seeing the fix is because our samples are not updated during the preview release. The fix will be available for the full 4.15 release.
In the meantime you can use the local fix by unchecking ‘Used with Skeletal Meshes’ which was the cause of the error message you are reporting.
I have updated the bug report to reflect the comments mentioned.