I have updated my OS to El Capitan, and all my scripts including MPgraph functions such as gdata do not work anymore (script without such functions are working without any trouble). 

Would someone know how to get rid of this issue?

I thank you very much.

a short code sample:

x:=u*1cm;

a1:=6;

a2:=5;

hauteury:=a1*y;

echelleMEP:=1/10*hauteury/a2;

gdata("explexpl.d",s,

y1:= scantokens(s1);

y2:= scantokens(s2);

draw (7.5*x, y1*echelleMEP)--(8.5*x, y2*echelleMEP) withcolor 0.6 white;

);

Cheers! 

Louis-Solal