There is no difference in the child support tables.  Everything should be identical.  You should very closely check that all the assumptions made with regard to income and parenting time adjustments are also the same.  There is most probably an error somewhere because the calculators should not be off by that much.  In fact, all things being equal, both calculators should get the exact same number.

There are, however, slight differences in how this calculator works.  This is because the guidelines leave a few things open to interpretation and are not clear enough.  One such issue is rounding.  You can search this site and read more about it.