I have the same problem and hope you get a reply else need to contact TurboTax for an answer.

Solved. Spent an hour with TurboTax support. Leave proceeds of disposition and adjusted cost base blank and just enter eligible amount of gift. This will clear the error message.

Thank you for your time!

No this solution did not work and seems dishonest as well

@agclark If you are seeing an error regarding "Eligible amount of gift on T1170" in the review, click on the "Fix" button and it should allow you to enter the amount. 

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