File does not exist: general.css

[Toxalot]

I see a lot of entries in my error_log for missing general.css for statistic pages.

Examples:
File does not exist: /var/www/vhosts/example.com/statistics/ftpstat/general.css, referer: http://example.com/plesk-stat/ftpstat/nav.html
File does not exist: /var/www/vhosts/example.com/statistics/webstat/general.css, referer: http://example.com/plesk-stat/webstat/nav.html

Why is this file missing?