2
Are you using XOOPS 2.2.x?
That message is apparently generated in include/checklogin.php:
redirect_header(XOOPS_URL . '/user.php', 5, _US_INCORRECTLOGIN[color=ff0000]. $xoopsAuth->getHtmlErrors()[/color]);
The method $xoopsAuth->getHtmlErrors() is in class/auth/auth.php.
I don't know what that's for, but you could temporarily change it to:
redirect_header(XOOPS_URL . '/user.php', 5, _US_INCORRECTLOGIN);