ipn_main_handler.php is a blank page

I'm using Zencart v1.3.9c

I'm using paypal checkout express.

Upon payment whn i click the paypal checkout button it directs me to https://www.mydomain.com/ipn_main_handler.php?type=ec but it shows a blank page on my browser.

Here is the log file I got from includes/modules/payment/paypal/log

Sep 28 2010 3:34 -- IPN PROCESSING INITIATED.
*** Originating IP: 122.52.108.196 122.52.108.196.pldt.net
*** Browser/User Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)

Sep 28 2010 3:34 -- IPN FATAL ERROR :: No POST data available -- Most likely initiated by browser and not PayPal.

 *** The rest of this log report can most likely be ignored !! ***

Sep 28 2010 3:34 -- IPN ERROR :: Could not find stored session {} in DB; thus cannot validate or re-create session as a transaction awaiting PayPal Website Payments Standard confirmation initiated by this store. Might be an Express Checkout or eBay transaction or some other action that triggers PayPal IPN notifications.

Sep 28 2010 3:34 -- IPN ERROR :: No saved Website Payments Standard session data available. Must be an Express Checkout or Direct Pay transaction.
Could be a test notification, or the incoming IPN notification is not actually a bonafide PayPal transaction.
NOTE: It is likely that all the following log content is meaningless or irrelevant.

Sep 28 2010 3:34 -- Breakpoint: 0 - Initializing debugging.

Sep 28 2010 3:34 -- Breakpoint: Flag Status:
isECtransaction = 0
isDPtransaction = 0

Sep 28 2010 3:34 -- IPN INFO - POST VARS received (sorted):
Array
(
)

I hope someone can help me with regards to this problem.

That is typical log content when you access ipn_main_handler directly from the browser, as explained by the messages within the log file itself.

hi DrByte... my bad,yes I did try to browse that file directly in my browser.

but do you have a solution for me, why I keep having a blank page after clicking the paypal checkout process?

A blank page generally means you're encountering a PHP error. That's usually a result of corrupt files, bad addons, incomplete FTP uploads, or just plain wrong editing of files.

https://www.zen-cart.com/tutorials/index.php?article=82