New customer entry not going to cart on checkout...

I just noticed that my shopping cart is not successfully going to the checkout screen or cart after a customer creates a new entry.

All I'm getting is a blank screen, no errors, nothing. If I refresh the screen, I get a red error box stating that the customer record already exists, and I can then continue to check out fine.

Testing with Chrome, but IE just did the same thing.

I see this in the URL at the top:
https://my_web_site.com/index.php?main_page=create_account
(fictitious site here)

Anybody know where I can start to debug this?

Thanks.

OK... been a long time, but I found the log files in \cache, and find this error:

[14-Aug-2012 16:48:48] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/my_host_site/public_html/includes/languages/english/create_account_success.php:18) in /home/my_host_site/public_html/includes/functions/functions_general.php on line 45

I'm now looking at the document that might have my answer... blank line at beginning of file... not sure which one, but I'll check both.

SOLVED!

I found a blank line at the end of ".../includes/languages/english/create_account_success.php"

Great resource here, just have to search a bit.