How to fix this error?

I received an email from my server with subject: Cron <[email protected]> /usr/lib64/sa/sa2 -A
and body: Invalid system activity file: /var/log/sa//sa13

Why this error happens or how to fix it?

I tried this: rename that file and then create new empty one:
Code:
mv /var/log/sa//sa13 /var/log/sa//sa13_old;touch /var/log/sa//sa13