Why would you think it is not taxable income?

I may be confused thus the question. code X says it qualifies for exclusion

When I look up code X  for 1099-B this is what I see

Code X. Use this code to report a transaction if you cannot determine whether the recipient should check box B or box E on Form 8949 because the holding period is unknown.

I don't see anything there about an exclusion, just that the issuer did not know the holding period of an uncovered security.

On the 1099B worksheet it states that code X is for DC Zone or exclusion. This sale shows no date acquired, no cost or basis and checked as Noncovered security only proceeds from sale in excess of $50,000.

Client or his financial advisor will need to provide some basis information before you can accurately file the return. (Unless they wish to report the entire sale as Gain).

You are looking at the Adjustment Code list, not the 8494 box code on the entry line just before the date sold.

Code x is on the 1099B. Client was able to resolve problem.

Thanks for youhelp.