I didn't roll out that upgrade (yet) but having a swift look at your message I think it might be that ubuntu distribution upgrade not in effect yet (no reboot, running on old core with new scripts?).
Again, never upgraded to different ubuntu server through zentyal dash yet, so I don't know whether It propagates or enforces reboot, in my update processes I always seperately had to reboot (running 3.4.8 now, zentyal for past three months or so).
If you didn't reboot after upgrade, try it manually via dash > system > reboot-halt or via ssh, that might solve your problem!
[edit]It literally means C library NET::LDAP (so the error is connected to your LDAP application) suffers errors while handling calls to it, probably version/compatibility issue, specially since after upgrading. try the reboot. hard C libraries are used p.e. with non statically compiled binaries. statically compiled means that binary includes these libraries in itself instead of relying on the OS for providing them functions.