Internal server error 500 VisitsSummary

Piwik 2.15, IIS 7.5, php 5.6.20
We have a high-load site monitored by this piwik
Reports set up Auto-Archiving
We have a report made by Widgetize and VisitsSummary in our site
When we get the report for the period of day everything works fine, but if we want to get it for week or month it gives error 500 about five or seven times. At the end we get the report and then the report is shown without any errors.
the link of the report is like this:

It looks like that when we click the report, piwik starts indexing or archiving or something else so this operation has a long time ending and when the operation ends the reports run without any error.

What should be done to get the report without error 500?


You need to setup the cron to pre-process reports, and get ultimate performance in Piwik: How to Set up Auto-Archiving of Your Reports - Analytics Platform - Matomo