I've downloaded and installed the constant contact custom form php application.
When I get to the setup / authenticate screen, my constant contact username and password is not accepted.
Please advise how I can get past this so that I can create my custom form.
I just did some testing with multiple accounts and did not receive and errors regarding correct credentials not working. Are you using the same username and password that allow you to login at constantcontact.com? Can you also paste the exact error message that the program is returning for you? If you were receiving notifications that the program had already been configured with different login credentials, this is a different issue.
If you could also provide your username, I'd be happy to take a look at your account and see if there is anything that may cause an issue with logging in. If you don't feel comfortable posting that on the forums you can submit the information to our webservices support team and we can continue this conversation through email.