dyn.load() returns "LoadLibrary failure" only in RStudio

I am trying to use CoolProp with RStudio on my new Win10 machine, as I was doing ever since on Win7. However I get this error:

Error in inDL(x, as.logical(local), as.logical(now), ...) : 
  unable to load shared object 'CoolProp.dll':
  LoadLibrary failure:  Eine DLL-Initialisierungsroutine ist fehlgeschlagen.
> 

The same works like charm in the R Gui (same R version, same platform).

I found people having traced back similar problems to issues with environment variables. I compared the output of Sys.getenv() for both, RStudio and RGui, without any obvious problems. Anyhow, I changed all variables in RStudio to the values of RGui - without success.

Below is the output of PATH.

Any ideas???

Thanks,
Eric

> Sys.getenv("PATH")
[1] "D:\\Users\\elaurenz\\Programme\\R\\R-3.5.3\\bin\\x64;C:\\Program Files (x86)\\Intel\\Intel(R) Management Engine Components\\iCLS\\;C:\\Program Files\\Intel\\Intel(R) Management Engine Components\\iCLS\\;C:\\ProgramData\\Oracle\\Java\\javapath;C:\\Windows\\system32;C:\\Windows;C:\\Windows\\System32\\Wbem;C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\;C:\\Windows\\System32\\OpenSSH\\;C:\\Windows\\wbin;C:\\Program Files\\IrfanView;C:\\Programs\\MiKTeX 2.9\\miktex\\bin\\x64\\;C:\\Program Files\\MiKTeX 2.9\\miktex\\bin\\x64\\;C:\\Program Files (x86)\\Intel\\Intel(R) Management Engine Components\\DAL;C:\\Program Files\\Intel\\Intel(R) Management Engine Components\\DAL;C:\\Program Files\\Intel\\WiFi\\bin\\;C:\\Program Files\\Common Files\\Intel\\WirelessCommon\\;C:\\Program Files (x86)\\Airtame;C:\\Program Files (x86)\\PuTTY\\;D:\\Users\\elaurenz\\AppData\\Local\\Microsoft\\WindowsApps;D:\\Users\\elaurenz\\Programme\\R\\Rtools\\bin;"ยดยดยด