Embedded SQL - Variable File Name

Why can't I do this?

C/Exec SQL         
C+ Select Sum(IOQTYO)
C+   Into :pWkQuan :WkNull
C+   From :MyFile  
C+   Where IOITEM = :pWkItem And
C+         IOWHSE = 'PH'     And
C+         IODELE <> 'D'
C/End-Exec         

Where MyFile is a variable. I get a "Token : was not valid. Valid tokens: (
TABLE LATERAL <IDENTIFIER>." message.

Rob thought it might be because there wasn't a space before my null
indicator variable, but that didn't seem to fix it. The statement was
syntactically correct (and worked too!) before I tried a variable file name.

How can I do this? Do I need a prepared statement with parameter markers?
Anyone have an example?

(Posted to correct list)

Thanks!