Child Sites not working after server migration

Hi,

My wordpress mutisite worked successfully for the last 3-4 months, recently after a server migration . it stops working…

i created two child sites say..
“site1.maindomain.com” points to “domain2.com”
“site2.maindomain.com” points to “domain3.com”

created the vhost files etc..

While accessing “site1.maindomain.com” and “site2.maindomain.com” its showing a “Server not found” error..
but if i access “someother.maindomain.com” its redirecting to a page in “maindomain.com” saying the following

Greetings Site Administrator! You are currently allowing “none” registrations. To change or disable registration go to your Options page.

I think i missed something.. Can u please guide me..

im using 1and1 linux servers with Plesk 10.0.1