New Post: WSUS Migration: Existing self-signed certificate becomes invalide

In WSUS-FAQ No. 44 you will find needed Updates for your new WSUS: http://wsus.de/faq

WSUS 3.0 (SP2): Build 3.2.7600.226
WSUS 3.0 (SP2) + KB2720211: Build 3.2.7600.251
WSUS 3.0 (SP2) + KB2734608: Build 3.2.7600.256
WSUS 3.0 (SP2) + KB2828185: Build 3.2.7600.262
WSUS 3.0 (SP2) + KB2938066: Build 3.2.7600.274

Update your WSUS first, reboot after the last patch and try it again.