Credit Card Error when processing Gift Certificates in 1.3.9f (worked in 1.3.8a)

Hi all,
i hope someone can help me with the following...

I've upgraded (did a full upgrade) zen cart from 1.3.8a to 1.3.9f.

files that I have uploaded from older version are as follows

/images/
/include/templates/
/includes/languages/extra_definitions/
/includes/classes/url_generate.class
/admin/include/languages/
/admn/include/boxes/
/admin/stats_export_orders/
/admin/specials.php
/admin/includes/boxes/extra_boxes/xsell....php
/admin/includes/extra_datafiles/xsell_definitions.php

/admin/includes/init_includes/overrides/init_hml_editor.php
/admin/includes/languages/extra_definitions/editor_list.php
/admin/includes/languages/extra_definitions/tiny_mce.php
/editors/tiny_mce/

Also I did a database upgrade patch via zc_install
and everything works fine (both on back end and frot end) apart from gift certifcates.

When Ordering a gift certificate ("Process payment") an error is thrown
"A credit card error has occured. Please verify your submitted details and resubmit. If this problem persists and please contact us."

and for the life of me i don't know the reason for this error. I assume it has to do something with the shipping. However, gift certificates are set up as per tutorial and, as mentioned, they worked fine on 1.3.8a version.

I noticed in changelogs for 1.3.9 that there were "Various fixes" on certificates/coupons so assume there were some changes in the code.

can someone please shed some light on this (where to look into the code? which files should I maybe copy from older version? do a diff??) as I am out of ideas.....

• it's Friday and as always this ######## happens on Friday.s.. and probably destroying my weekend.

thanks

mmm..anyone?