Time of day as fatnutritionist said is a good point.
Just about anything can cause sensitivities for some people. Iron is a frequent problem. I would suggest that sensitive people first find an 'iron free' multiple.
Softgels also can make a difference, but not with hard-to-digest soy oil as by GNC. Now Foods Liquid Multi Gels with flax oil is a nice formula. Suggested dose 2 per day, so if you take only 1 this will be low-dose as Creak seems to desire. This does contain iron, though a special non-constipating type.
I don't put much stock in the original one-a-day. Might as well eat a piece of liver or a spoonful of yeaast. Or go natural by taking separately:
spirulina capsule or powder for beta carotene
liver capsule for b complex
ascorbate buffered C pills
calcium citrate with magnesium and D
(best to take calcium only with meals and only in the afternoon)
use body lotion containing vitamin E
for potassium eat ripe bananas or take Krebs magnesium-potassium by Enzymatic Therapy
(Obviously many people will not want to 'go natural' by using so many things but just a possibility to consider.)