Upgrade from 1.51 to 1.54, Admin Works OK but store does NOT work with php >5.4

My site was upgraded from 1.51 to 1.54 week ago. Now Admin works perfect with all php versions while my site does NOT work with php versions >5.4. The site works perfect with php 5.3 and 5.2 ONLY. The database was initially upgraded from 1.38 to 1.39 to 1.51 and now to 1.54.

When I changed php version to >5.4 via cPanel, the home page of my site is fine but got blank pages during checkout shipping/payment etc. The Admin is fine for all php versions. Any suggestions? Thank you.

Blank or partial blank pages: http://www.zen-cart.com/content.php?124-blank-page

Thank you. I checked the logs and it shows "PHP Warning: Cannot modify header information - headers already sent by (output started at /public_html/includes/configure.php:1) in /public_html/includes/functions/sessions.php on line 115... But the thing is the 1st line of configure.php is just <?php which is nothing wrong.

On the first line is there either a blank line or a space in front on the <?php at the top of the file?

It is working now. Thank you all. I guess the text editor like NotePad++ has bugs and introduced unwanted space or line into the 1st line of configure.php. I copy and paste the configure.php to a new text file and save as configure.txt. Then the configure.txt was uploaded under public_html>includes. Deleted configure.php and change configure.txt extension to .php. It is working like a charm now with php 5.4, 5.5 and 5.6. The forum is very nice. Thank you all.

SignaGen2:

It is working now. Thank you all. I guess the text editor like NotePad++ has bugs and introduced unwanted space or line into the 1st line of configure.php. I copy and paste the configure.php to a new text file and save as configure.txt. Then the configure.txt was uploaded under public_html>includes. Deleted configure.php and change configure.txt extension to .php. It is working like a charm now with php 5.4, 5.5 and 5.6. The forum is very nice. Thank you all.

Glad that it is, though I wouldn't say that it was notepad++ that randomly inserted an additional character to a file. Being modified by the user... There are plenty of others that use notepad++ without it randomly introducing anything before the <?php at the start of the file...

But yeah, got it working.. Good luck!

Today I got another issue during checkout payment. Checkout by credit card (Paypal Payment Pro) with 2 items, the checkout confirmation page is total blank.

The log file shows:
It turned PHP Warning: Invalid UTF-8 sequence in argument in /ajax.php on line 24.

Any suggestions?