Error: The variable $FEATURE is unbound.



I get the following weird error message... anyone can explain what it means?


(C1) ode2(d(y(x),x)=1/y(x),y(x),x);


Error: The variable $FEATURE is unbound.
Fast links are on: do (si::use-fast-links nil) for debugging
Error signalled by MACSYMA-TOP-LEVEL.
Broken at MACSYMA-TOP-LEVEL.  Type :H for Help.
MAXIMA>>