It could be due to the state of the infrared LEDs. If your camera is blurry at night, then make sure you clean the LEDs thoroughly. If it is an indoor camera, you may have lots of fingerprints on them. One of the drawbacks with an outside camera is that it will have entrails of many creatures that have crawled over it! It may also be due to reflections from a nearby object. Check around the area of the camera to identify where the reflection is coming from and remove it, or block it.