I'd try remaking the session table ...
Be sure to have the structure to remake it taken from the v1.3.8a version of Zen Cart mysql_zencart.sql ...
NOTE: if you are using prefixes, and it appears that you are, this will need to be altered ...
DROP TABLE IF EXISTS sessions;
CREATE TABLE sessions (
sesskey varchar(32) NOT NULL default '',
expiry int(11) unsigned NOT NULL default '0',
value mediumblob NOT NULL,
PRIMARY KEY (sesskey)
Also, check your two configure.php files on the server:
Make sure that both are using the same database/username information ...