[NTG-context] metafun transformation error

Hi all, I am new to context and need help in solving an error. I am trying to print some numbers in a grid onto a transparent sheet as mirror images so that the numbers are correctly displayed when I view it from the non printed side. The numbers have a particular sequence which cannot be obtained from calculations. So, they are stored in an array of strings : l[0][0] := "38"; ... I place them at the centre of the grid squares using the code below:  for i= 0 upto (row - 1): for j= 0 upto (col - 1): middle := 0.5[((( i * unit) + lm), ((j * unit) +  bm)), ((((i+1) * unit) + lm), (((j +1) * unit) +  bm))]; p := thelabel(l[j][i], middle);  draw p; % q := p reflectedabout (0.5[urcorner p, ulcorner p], 0.5[lrcorner p, llcorner p]); % draw q; endfor endfor This works as expected. But, when I try to reflect the label by means of the commented code, I get an error :  tex error       > mp error on line 643 in file /home/ajith/Desktop/PlayGround/numgrid.tex:

...

(xpart T_,ypart T_,-0.00581xpart T_+0.00497ypart T_+0.15294,-0.00497xpart T_ -0.00581ypart T_+0.98824,-0.00497xpart T_-0.00581ypart T_+0.98825,0.00581xpart T_-0.00497ypart T_-0.15294) ! Transform components aren't all known. <to be read again> ; ...lcorner.p];q:=p.reflectedabout(uq,lq); draw.p; ENDFOR ...=p.reflectedabout(uq,lq);draw.p;endfor ENDFOR <*> ...lectedabout (uq, lq); draw p; endfor endfor StopPage ; ; I'm unable to apply a partially specified transformation except to a fully known pair or transform. Proceed, and I'll omit the transformation.

I tried a mock example without the loops and that didn't throw an error. How can I make it work within the loops?  Thanks, ajith