Analyzing the apache error log, The following errors are getting shown:

...........
[Wed Jul 27 12:39:13 2016] -e: Can't opendir(/opt/otrs/var/tmp/CacheFileStorable/DynamicField/a/3/c): No such file or directory
[Wed Jul 27 12:39:13 2016] -e:  at /opt/otrs//Kernel/System/Cache/FileStorable.pm line 227
[Wed Jul 27 12:39:13 2016] -e: Can't opendir(/opt/otrs/var/tmp/CacheFileStorable/DynamicField/a/1): No such file or directory
[Wed Jul 27 12:39:13 2016] -e:  at /opt/otrs//Kernel/System/Cache/FileStorable.pm line 227
[Wed Jul 27 12:39:13 2016] -e: Can't opendir(/opt/otrs/var/tmp/CacheFileStorable/DynamicField/0): No such file or directory
[Wed Jul 27 12:39:13 2016] -e:  at /opt/otrs//Kernel/System/Cache/FileStorable.pm line 227
.............

Those errors always occur after open a new ticket and choose a service.

Running OTRS 4.0.15 on a CentOS 6.