Singular

Hi there! I installed Singular wit cygwin and surf (Singular works, surf is in path).
When I run this manual sample:

LIB "surf.lib";
// --------- plane curves ------------
ring rr0 = 0,(x1,x2),dp;
ideal I = x1^3 - x2^2;
plot(I);

I get back:

Unable to start 'C:\cygwin\tmp\surf.jpg.jpg': The specified file was not found.
? calling `surf` failed
(The shell returned the error code 256.

Many thanks!