The variable types appear to be case sensitive, so byte, not BYTE. Also you use string, not CHAR.
(PHP 4 >= 4.2.0)
w32api_deftype — Defines a type for use with other w32api_functions
You need to call this function if you would like to define a type for a w32api call.
The name of the type.
A member type can be a user defined type. All the type names are case sensitive. Built in type names should be provided in lowercase.
The member name of member1_type.
This function takes 2n+1 arguments, where n is the number of members the type has. After that is the type of the member followed by the members name (in pairs).
Returns TRUE on success or FALSE on failure.
This function is EXPERIMENTAL. The behaviour of this function, its name, and surrounding documentation may change without notice in a future release of PHP. This function should be used at your own risk.