Material won't compile properly

For some reason my landscape material won’t compile properly, and it just leaves me with the default checker shader.

Here is the specific part that makes it break, the highlighted part within a material function. I get no errors, and this should work correctly right?:

Here is the master material:

Edit: Found an error within the material instance saying the maximum ps_5_0 sampler register index exceeded, what does that mean?:

Used the shared samples, learned new things today.