In php 5.5 preg_replace is deprecated. This leads to error messages being posted on the site and in the logs.
I am not too good with php, so I am wondering if someone can create an update. It seems to be the Sources/Load.php file that contains several preg_replace functions.
https://www.simplemachines.org/community/index.php?topic=534915.0
You should upgrade to current version, 1.1.x went eol some time ago and is no longer supported. Other option is to downgrade php to 5.4 (also eol and unsupported).