From the FAQ. Also number 1.5.29

Blackguard cannot be used to force the Corporation to rez an Archer.

Page 11, Column 2, Paragraph(s) 1, FAQ
The Runner has Blackguard installed an exposes an Archer. Is the Corp forced to rez the Archer?
Blackguard only forces the Corp to pay the rez cost, if able. The Corp does not have to rez the Archer and pay its rez cost because he can decline to pay the additional cost of forfeiting an agenda.
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