Are you or they getting any errors? If so, what is the error. More details on what you are experiencing would be helpful.
The only suggestion I have with the info I have is to go in to manage your clan and then choose to create a new link on the right side. Then give out that link and see if it works.
How many members do you have? Elite had an issue that if you had 98 members and 2 pending applications then you couldn't receive any new applications. Not sure if that applies to your situation, just throwing it out there.