I am posting this to help others that may encounter a similar problem.
Warning: Unexpected character in input: '\' (ASCII=92) state=1 in .....
Problem was explained in this issue
If you are still running on PHP 5.2 you should use the backported version of Predis and not the mainline library which targets only PHP >= 5.3 (the backslash is the namespace separator in PHP 5.3).
More discussion of this change can be found here.