This is my solution:
vars a,c,d;
init 1;
labels 0:a,c;1:a,c,d;2:a,c,d;
transitions 0->0;0->1;1->0;1->2;2->0;
This was your solution:
vars a,c,d;
init 1;
labels 0:a,c; 1:a,c,d; 2:a,c,d;
transitions 0->0; 0->1; 1->0: 1->2; 2->0;
You can see that your third transition wasn't ended by a semicolon but by a colon.