i) Check for the 'defaultdomain' in 'domain xml' file(got using ipsadmin command) and 'platform.conf' file are the same.
ii) Also check the domain xml to see if the URL Mapping list has the corresponding URL that you try to access.
If there are any mistakes, modify the xml file and reimport the xml file again using ipsadmin. Then restart the Server and Gateway.
iii) On certain occasions if the Server and the Gateway are not in sync with eachother we may get 'no such domain' error. Here restart of the Server and Gateway should help.
And if the problem still exists we need to have a look into the iwtGateway, iwtSession and iwtProfile logs.