Running requires different muscles than cycling, i.e. hamstrings are required much more. Even when the same muscle groups are used the firing sequence and tensions will be different between the two exercises. The shock absorbing the body endures from running, and probably the extra shock due to your cycling fitness and lack of running, may be part of the reason you have muscle soreness. If you intend to continue running, ease into it and do it more frequently. Possibly cut one of your rides short then do an easy short run for 5 or 10 minutes while concentrating on being smooth and not jarring. You may have the CV fitness to push yourself but your body will need time to adapt to the changing stresses. It may take a week or two to make the conversion. Back when I coached HS track and field the basketball players and swimmers would join the team late and would have similar issues.