login page problem (possible bug?)

I'm using version 1.3.7 and came across a problem when going through my site today. When I click the login button when there are items in my shopping cart, under the "Please Sign In" text it says HEADING_NEW_CUSTOMER_SPLIT and then shows the paypal exress button then more code lines. I've traced the text as coming from the tpl_login_default.php file and I've tried uploading the untouched version from the original files and still come up with the error. I can login to an already created account, but it doesn't allow me to create a new customer. The error does not show up when there are no items in the shopping cart so I can only conclude that something is happening inside of the <!--BOF PPEC split login... --> (line 20). What can I do to resolve this? Thanks for your help. You guys are awesome!
Oh, if you want to see it in context the page is located at http://www.jumprm.com/shop/index.php?main_page=login I added a couple lines explaining an error is happening, but didn't touch any of the code to do so. Like I said, it only happens when there are items in the shopping cart.

was this an upgrade or fresh install?

have you made any changes to any language files?

if not then try to upload the includes/languages/english/ folder again,

It's an upgrade from 1.3.6 I solved part of the problem and am looking for the remainder. On the change log in the upgrade instructions it didn't say the login.php page had changed since 1.3.6 but it had. That took care of the top part, but the link for the create account button is messed up and I'll get that solved soon. Thanks for your help, there's so many files to look through it speeds things up considerably when I know where to look.