Hello, his error most likely had nothing to do with the SHA1-sign (solution suggested by DesignHaus42)
I am currently using Prestashop 1.5.3 with the Ogone plugin 2.4 (latest) and it still has this bug.
When people pay by using bank transfer, the status changed to "Payment Error" rather then "Pending Payment". All other payment methods work just fine.
Is there any solution to this problem?