Set debug = False in /etc/fts3/fts3rest.ini and restart.
If you have several FTS3 instances behind a DNS load balancer, then you have two options
Generate one single certificate with the public name, and share them between the different hosts. This solution is suboptimal, since then each host will not be accessible separately.
Issue one certificate per host, with the subject matching the host name, and add to all of them a subject alternative name that matches the balanced name.
The X509v3 extension handling in the python26-m2crypto shipped in EPEL5 is broken, so it has been disabled. If you are getting this error in some other platform, please, let us know!