Symptoms:
Array operations producing parse errors in code that was previously working.
Parse errors in commented out code.
Cause:
A back quote (key left of 1 on US standard keyboard) had accidentally been added on a line.
Solution:
Find and delete that sucker!
This took me all morning to track down. I finally had to resort to the debugging method of removing and re-adding code block by block. I am posting this here so that no one has to go through that again.