Running per se ain't bad, it depends on how often you do it, intensity, etc. Not knowing anything more about your background, maybe you jumped into it too fast and injured yourself.

I mix bicycling and running each week. My rules are similar to what has already been mentioned: 1) no pavement 2) take it easy (no crazy, rough or steep terrain), and use good shoes. Runs are 3-5 miles 2X per week, and three biking days of 20-30 miles each (sometimes a longer 40-50 mile ride on weekends
).