The 1099-b I received has "Unknown" in box 1b Date Acquired and 1e Cost Basis. TT is not accepting "blank" for box 1b and no entry for box 1e. How do I proceed?

If you don't know the basis, it would be a good idea to try to find out what it was. If you have no dollar amount to include, your basis defaults to zero and the entire amount of the sale becomes taxable.