You haven't provided a lot of information. For instance, have you ensured that you are selecting the sRGB color spaace as part of your print set up? Are you choosing the appropriate paper profile? Are you soft proofing and using the appropriate paper profile? You indicate that this happens "sometimes". Can you identify what seems to trigger the problem? What operating system are you using? What printer are you using? What exact version of Lightroom are you using?