The version number 5.7 refers to the ide, the editor, the current product version of the HC12 is 4.7,
so I'm basically don't know what you are using, its not 4.7 as this version ships with an IDE 5.9.
Anyway, the LDW is not a real XGATE instruction, it is a pseudo instruction which generates 2 actual instructions when assembled. The support for LDW is mentioned in the release noted of the 4.7 release as new feature, so I guess you are using an older version which does not support this pseudo instruction.
With your version, use the actual assembly instructions instead:
Code:
LDL R4,#$34 ORH R4,#$12
Daniel
BTW: I don't like those pseudo instruction, especially with assembly I like to see things explicitely.