I am attempting to plot an initial value problem in Maple 18. I have my equation defined, as well as a general solution and two particular solutions at y(0)=3/4 and y(0)=1/2. To graph, I entered the command

DEplot(de,y(x),x=-3..3,{[0,1/2],[0,3/4]},dirgrid=[12,12],color=black,linecolor=blue,thickness=2);

but instead of returning a graph, the software gave me the error message

Error, (in DEtools/DEplot/CheckDE) extra unknowns found: sinx

The Maple support site lists this as an unknown error, and as a new user, I'm not sure what to do. What does this mean?