Warning: preg_match()

I run cron from in my website and I get

"Warning: preg_match(): Compilation failed: nothing to repeat at offset 0 in file_scan_directory() (line 2278 of /home/topexp/web/mysite.com/public_html/core/includes/file.inc)."

37 times

I have installed the latest version of backdropcms and 3 modules akismet, honeypot and filecache.

Any ideas?