lmpr in assembly

ive got this peice of code which wont run due to lmpr not being recognised by the assembler. im using comet 1.8. here is a snippet of it:

ORG &E000  ; In the space after a screen in HMPR
              LD  (SPSTORE),SP
              LD  SP,STKSPACE
              IN  A,(LMPR)
              EX  AF,AF'      ; See below
              LD  A,%00101011 ; Page 11 with no ROM
              OUT (LMPR),A
              LD  HL,(SCROLLPOS)
              LD  DE,&8000    ; Top of screen - you could change
                              ;  this to another area.
              LD  IX,OFFSETS
              LD  B,32        ; No. of lines in top half

any ideas?

The assembler doesn't inherently know about the names of Sam's registers, you need to define them as symbols with a line such as: