can anyone tell me what is wrong with my subdomains?

[Jog Dial]

Hi,

I have setup two subdomains from my domain.  My domain is

emtex.com

The subdomains are

uk.emtex.com
us.emtex.com

Some mailers are still refusing to send email to us saying
non-existant domain.

I have tested both of subdomains using dig against both nameserver,
ns.emtex.com and ns.cerbernet.co.uk and they both come back with
noerror.  Can anyone see what is wrong?  Many people can email us... a
few can't.  I have been looking at this for 3 days and thought I had
it all working ok last night, but then someone again had problems
today.  Could they have bad cached data?

Thanks for your help.  I've gotta run right now, if you need zone
files etc, I can post them later...