Thankyou for your suggestions but I'm still not managing to fix this.

I have enabled now youtube in google apps.

When I try and login to youtube I use my email address and password.

I am then taken to a screen saying 'Do You Already Have A Youtube Account?'

I insert my username and password. It tells me my password is incorrect, so I click on cannot access my account.

Password reset information is emailed to my account.

I click on reset password, enter my email address and the captcha and I am taken here:

https://www.google.com/support/accounts/bin/request.py?hl=en-GB&contact_type=acc_reco&ara=2&ctx=acc_reco&source=no_ts&rd=1

(a help page)