user or group name resolution in crsoss forest with two way trust

Hi

i am setting up platform for cross forest migration.
all done i am able to access resources in both forest.

here is issue.

"ordernet" is 1st old forest
"orderline.com" is 2nd new forest

two way trust relation is completed.

when i try to add users to group in 2nd from 1st it works.
when i try to add users to group in 1st from 2nd after selecting the forest
it does not resolve the is it due to single lable domain or what please help
since i have to do this over weekend.

Thanks
Imran.