Error "Can´t find or open file" pops up when working with a VST

Hey folks,
 
there is an error I am dealing with since several weeks now. There is a popup which appears on any project I´m working with, as soon as I´m working with a VST:

This is in German and the translation would be like: "Can´t find or open file"
 
It doesn´t matter if it´s Kontakt, AD2, Dimension or any other VST.
 
This happens on following scenarios:
- Unfreezeing a VST
- Loading (doubleclick) on a programm in Rapture
- Randomly appearing when working with a VST
 
This is definetly a VST-related problem. Freezing/unfreezing a Audio-Track is causing no such error.
 
At first I thought it´s an error that came with the last Sonar-Update and will disappear with the next but this message keeps  comming.
 
That´s my setup:
Sonar Platinum x64 - 22.9.2 BUILD 42 [2016.09]
Windows 10 x64 (10.0.10586)
Intel Core i7 4th gen 3.33 GHz
16 GB Ram
Roland Studio Capture UA-1610
 
I have Windows and Sonar installed on a SSD M2 (C:\). My profect files are on a RAID10 (F:\cakewalk projects\)
 
I already gave my plugin-folders full permissions (read/write) in the Windows-Explorer-Settings.
 
Any suggestions?
 
Cheers,
andy