Blkproc and inline function

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Hi,
It's my first fight with Octave (after SciLab) and I've some trouble 
with using blkproc function.
When I pass function inline, like this blkproc(image, [16 16], 
'P1*x*P2', T, T') I've got error like this:
"error: feval: the symbol `P1*x*P2' is not valid as a function".

T, T' - arrays (P1, P2 parameters just like in Matlab).

Is there any  trick to pass  this (P1*x*P2) function to blkproc without 
error?
Thx.

--
Pawel