This W-level message alerts you to what is at best poor programming and at worst a source of problems. The message produced by the new compiler looks like:
IBM1091I W FIXED BIN precision less than storage allows.
The Enterprise PL/I compiler will produce this message whenever a SIGNED FIXED BIN variable is declared with a precision other than 7, 15, 31 or 63 or whenever an UNSIGNED FIXED BIN variable is declared with a precision other than 8, 16, 32 or 64. The compiler will also issue this message if a built-in function such as BIN, ADD, DIVIDE, etc has a FIXED BIN result but specifies one of the above precisions.
For example, if you declare a variable as FIXED BIN(5), the compiler will flag the declare, and you should probably change the declare to the intended FIXED BIN(15).