There are two zencarts vision1. 3.6 on my old server detail :
HTTP Server: Apache/2.2.2 (Fedora)
PHP Version: 5.1.6 (Zend: 2.1.0
New server :
Server: Apache/2.2.9 (Fedora) PHP Version: 5.2.6 (Zend: 2.2.0
Both use plesk 8.6
Use migaration tool inside of plesk move website from old to new server .
Both zencart can not log in admin area .
Then reinstall fresh copy of zencart version 1.3.6 have same problem .
Reinstall fresh copy of zencart version 1.3.8 use update database from 1.3.6 can log in admin area .
What I think problem is php 5.2.6 with zencart
I need move whole site from old server to new server without any problem . you may need downgrade php version . and whateven other job you may need to do to made that happen. will pay only after test 100% sure no problem .