Always invalid regex

I whant to remove some dates form a field so I tried to add REGEX find replace.
I filled regex pattern with
/(19|20)\d\d[- /.](0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])/
And left the rest blank assuming that that will remove dates. Yet I am getting
Invalid regular expression.
Message and for me the expression seams fine. What could be the case?