Hi,
Without seeing your shader, it would be hard to tell what's going on. However, from the error message, it sounds like your shader assigns an array of vec2 values to a float. We have been doing quite a bit of work in our shader compiler in order to pass some tests that include negative cases (ensuring that we don't compile illegal shaders).
If you could post the shader, or at least the line generating the error, we can see where the problem is.
As for the increased CPU usage, you are right. CPU usage should not be high if the GPU is the bottleneck. We will investigate.
Thanks,
Graham