Ok so I just had a brain wave and sorted this issue out for myself.
The brain wave was as follows:
my main solarwinds box can talk to most of my pollers but not some newly added ones, even though the new pollers can communicate to my main solarwinds server and SQL server as I had to add enteries into the host file for these to work as they were in serverate domains.
So from my new poller I can telnet on port 17777 to my main solarwinds server without issue, but the reverse (main solarwinds to new poller) would not work using the host name. If I used the FQDN name the communication from my main server to my new poller worked.
The solution was to add the IP address and hostname of the poller to the HOSTS file on the main solarwidns server. Now I can telnet on port 17777 from my main solarwinds server to my new poller without issue and my license details screen now shows no issues!
Thought I would just post up how I fixed this incase anyone having the same issue stumbles across this article