thanks for replying Mike,
this is the exact error message:
Your form submission contained the following errors:
The links page file name cannot contain the following terms: link, links, exchange, 3way, threeway, three
Please click the BACK button of your browser and correct these errors before continuing.
I have also made sure that both the links page and the data entered in the relevant fields are the same as I copied and pasted it.
Update: I've just added the page name and not the entire url i.e. mydomain/extensionhere and it has been accepted.
Phew

Thanks anyway Mike!