do you know what type of sealer was used?
I have used a stripper from custom Building products to remove sealers that were used on tile and grout surfaces...this was done as part of an overall cleaning and restoration effort.
This may work for you here as well...test is out in an area..if it does the trick great...get it cleaned up and then you can re-apply a better product.
You need to find out what type sealer was used.
If its an outdoor area, its most likely a solvent based material. To check, put some Xylene on a rag. (wear gloves) and see if the coating re-emulsifies after exposure. If it does, its a solvent based material. If not, its most likely a waterbased acrylic. As the above state, you have to apply like material over like material.