Ok, I just did some testing on my project. I loaded it in saved it under a different name (added "-Pbob" to filename) then converted all Bob instructions to Pbob. Everything worked until it found the first Pbob instruction then it flagged an error.
Confused, I dug up the Pbob documentation. I found the following:
Pbob NR,X,Y,IMAGE
 Does almost the same thing as the normal Bob command.
 The only differences are :
 1) the maximum width of the IMAGE is 32 pixels wide.
    There are no restrictions on the height of the Pbob.
 2) the height of the IMAGE that will be displayed may NOT exceed
    the maximum height for this Pbob.
    See the Pbob Height command.
 3) the amount of colours of the IMAGE may NOT exceed the amount
    of screen colours where the Pbob will be displayed.
    Else a crash is certain!
    So if you open a screen with 4 colours, do not try to display a Pbob
    with 8 or more colours. But it is valid to, for example, to open a screen
    with 32 colours and	display Pbob's with fewer colours (bitplanes).
    Only the bitplanes defining the Pbob will be copied on screen.
    
 4) all parameters must be included.
 5) the Pbob numbering starts at 1, not 0 like the AMOS/Pro Bobs...
 6) it is important to know that the coordinates for the Pbob's are
    measured from the top left-hand corner of the image.
    The current hot spot setting in not taken into account!
 7) the Pbob commands have to be executed in the screen where they are
    to be displayed !
    This is because a part of the Clipping routine is done inside the
    Pbob command.
    Ex.:
	Repeat
   	   Screen 1
	   Proc UPDATE_SCORE
	   Screen 0
	   Proc MOVE_BADDIES : Rem move the BAD_GUYS with Pbob NR,X,Y,IMAGE
	   Proc MOVE_GOODIE : Rem  move the GOOD_GUYS with Pbob NR,X,Y,IMAGE
	   Proc UPDATE_BADDIES_AND_GOODIES : Rem Pbob Clear : Pbob Draw : Screen Swap : Wait Vbl
	Until AMOUNT_OF_GOODIES=0
My bob images are 60x60. So that's why it won't work with my existing bobs.