Redmine

recently , I migrated redmine-2.3.2 from one machine(ruby 2.0.0-p247 centos6) to another(ruby 2.0.0p353 rhel7)

I installed the ruby gems, dumped the mysql database ,and then copied the redmine directory, and finally run it with apache+passenger

everything seems ok except that:

some people find that sometimes their session become another one's, for example:
A login as A, but after a while, when he reload the page, the login account become B

I did "rake generate_secret_token" and restarted apache, but it was no use.

any one can help find out what's the problem?