A friend asked me if he should receive Communion if he was in doubt about whether he had committed a mortal sin. I told him that he should not, but he did anyway. He later went to confession and told me the priest said he did the right thing by receiving the Eucharist, even when in doubt as to whether he should.
Receiving Communion when in doubt as to whether or not you are in a state of grace is not the same thing as receiving Communion while in a state of mortal sin. If you sincerely are in doubt as to whether or not you are in a state of grace, then there is a possibility that you might be in a state of grace. If that is the case, then I cannot see any reason not to receive Communion, so long as the person goes to confession at the next reasonable opportunity to confess his sins and discuss his doubts with the confessor. This is particularly so for a scrupulous person who may struggle daily with certainty over whether or not he is in a state of grace.