Possible causes:

1. Inadequate blade tension
2. Incorrect guide block adjustment
3. Poor blade tracking
4. Worn belts
5. Dull blade
6. Feed rate too fast

Solutions:
Same as above:

1. Tighten the blade (p. 38)
2. Adjust guide block gap (p. 36)
3. Adjust tracking (p. 30)
4. Install new belts (p. 39)
5. Install new blade (p. 38)
6. Slow feed rate