After a little time, when Visual Client is running a Windows dialogs pops up. The message is "Missing system file perfc009.dat, go to supportpage of..."

What does that mean?

This mean that the WMI of the operative system is corrupt which happens from time to time. This part is concerning "performance triggers" which is the part of the system that keeps tracks of changes in the system (which VisualCron uses).

What you need to do is to perform a "repair" of the WMI. Various links on google help with how to repair WMI.

Search on "repair wmi".

For example this link:

http://windowsxp.mvps.org/repairwmi.htm 

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