I installed a new shower enclosur and forgot to put the drain assembly in before mounting the shower. How do I solve this problem?

What brand of shower pan did you install? Some do not require prior installation of the drain. Plumb-Rite's Wingtite. "Replace the Drain, Not the Whole Shower (http://www.plumbrite.com/?page=faqs) Might be of great use to you at this point.