That is a very very old version and a very old bug ...

I don't have that version even setup ...

If you download Zen Cart v1.2.7 and compare the /includes/application_top.php there is a line in the section for the customer authorization that included additional pages that could be run ...

This might help you resolve this ...

NOTE: it is highly recommended that you upgrade to at least v1.2.7 ... there are bugfixes and security issues that have been addressed since that ancient version that you are running ...